This is definately an area where the performance gain from a modification is directly related to the price.
More suspension travel means the truck is more likely to stay planted with four wheels on the ground, keeping traction and decreasing the likelihood of getting stuck, lifting wheels, or flopping.
Front
Low-Profile Bump Stops
This is the cheapest, easiest way to get almost an inch of useable compression. An inch might not sound like much, but for an IFS rig, almost an inch is a lot. They're about twenty dollars, about half an inch thinner than the stock stops, polyurethane, and they're even bling bling red. Installation requires only a large adjustable wrench to remove the stock stops if they're stuck, the new stops can be threaded in by hand (use grease if you ever want them out again).
Longer Shocks
A longer shock allows more extension. Some spacer kits include a small spacer which fits on top of the coilover assembly, effectively making the shock longer. Some coilover replacement kits include a shock with a longer shaft. Either way, be
absolutely sure that the shock cannot extend the suspension beyond the maximum angle of the upper ball joint. The UBJ is extremely small, particularly at the neck where the stud meets the ball (hidden by the grease cover, pull it up for a look). Certainty can come from a properly sized shock or a limit strap. The upper ball joint is not capable of much more angle than the stock shocks allow. Solutions cost between a couple hundred bucks for a spacer or a simple, non-rebuildable shock with a longer shaft, to roughly a thousand dollars for complete rebuildable coilover assemblies. Bilstein currently offers a version of the 5100 shock, intended to replace the stock shock and use the stock spring, but with a slightly longer shaft to take advantage of the entire range of motion of the stock upper ball joint.
Uniball Upper Control Arms
Replacing the stock upper ball joint results in the greatest potential increase in front suspension travel for a Stock-class Tundra, with a vertically mounted, single shear uniball providing roughly 4" useable droop over the stock UCA. In order to capitalize on the additional travel available,
the truck must also be equipped with a longer shock. Depending on the suspension configuration used, limit straps may be necessary to prevent the uniball from becoming the extension limiter, as the friction between the ball and socket from the force of the coil spring will prevent the wheels from turning and can damage the uniball assembly, as well as bend the single-shear main assembly bolt. The proper limiting component is either a strap or the shock, if the shock is equipped with an internal limiter. On ABS-equipped trucks, the sensor wire needs to be secured in such a way that it neither rubs nor interferes with movement of the arm. In addition to the increase in articulation range, the pivot point is raised from the top of the spindle to the side of the UUCA, and the side of the UUCA is narrower than the stock UCA. When the suspension droops, the tire is pulled toward the stock UCA and may rub the arm. The raised pivot point and lower profile of the UUCA results in a near-constant distance between the tire and side of the upper control arm, and more clearance to the arm than the stock UCA (not accounting for tire flex).
Rear
Longer Springs
A longer leaf spring will allow the rear axle to droop further (a softer spring will also allow more droop, but the reduction in payload is usually a critical downside). This requires a complete new spring pack, generally running around five hundred dollars from a good manufacturer. Since length is measured along the arch, a lifted spring is a longer spring, so the stock spring and shackle mounting points do not need to be changed. A longer brake line is required for longer springs, and the ABS sensor wire(s) will need to be adjusted to provide slack at maximum droop on trucks so equipped. The emergency brake cable hanger at the aft end of the frame may also require modification to prevent the housing from becoming a travel limiter. Note that a longer spring also requires a longer shock to be able to use the additional travel from the new spring.
Uniballs (Again)
A normal leaf spring has a rubber or polyurethane bushing at each end to allow some degree of twist when the axle moves. These bushings wear every time the rear axle twists, and the spring pack wears as well as it's being twisted between the frame and axle when the rear articulates. Replacing the bushing with a ball and socket assembly allows the spring pack to remain nearly perpendicular to the axle during articulation, removing the need to force the pack to twist as well as extend or compress. This requires a wider spring perch and shackle, the spring and ball/socket assembly are sold through
Alcan Spring as "Orbit Eyes".
Some Notes Regarding Spring Rate
One of the two most important considerations for your suspension is the rated weight of the springs (the other is the valving in the shocks). This is the recommended load that must be applied to the spring in order to achieve the most flex--too much, and the spring is overcompressed; too little, and the spring won't flex. A common complaint used to be that the tundra rides "too soft". This is the mark of a well-engineered spring, matched to the weight of the stock, unloaded truck. Bouncing results from a lack of adequate damping by the shocks, not an incorrect spring rate. Larger trucks ride rough when empty because the leaf springs are built to carry a heavy load, at which point they will ride as smooth as an unloaded Tundra.
Read this FAQ from Alcan Spring, specifically the section entitled
"Do Alcan springs ride soft?", as the explanation is general and applies to any spring whether coil or leaf. When considering an upgrade to the springs, keep in mind the weight the truck will carry. While a stiffer spring may make the Tundra ride "more like a truck", keep in mind those other trucks ride like they do because of their intended ride quality at their intended payload weight. A car doesn't have the intended working payload of a truck, allowing the suspension to be tuned to the weight of only a few people (~200#-800#), not a few people and a half ton of whatever in the back (~200#-1800#). A stiffer spring will allow the truck to carry a heavier load (ie winch bumper & winch, recovery & camping gear, etc.), but the truck will ride rough until you add the weight--articulation is reduced, ride comfort suffers, and the truck is subject to more shock loads more often, meaning more squeaks and rattles. Evaluate your needs carefully before purchasing new springs.