I have a 2001Tundra 4x4 Access Cab 4.7l. It has high mileage (225k), but, has run great since I bought it about 10,000 miles ago. Last week I drove to Albuquerque, a 1600 mile trip one-way, I loaded a small trailer and towed it back home. About halfway back the truck began missing when it was put under any strain, the check engine light came on and flashed when it was actually missing, but I continued on. When I got home I went to Auto Zone and they said it was reading multiple misfires on cylinders 5 and 7. I replaced the spark plugs, which needed to be done badly, and reset the code. It ran great for about 60 miles when the check engine light came on again, it then started to miss again when accelerating lightly at speed. Went back to Auto Zone and this time it was a P0430 code. Any ideas on what to do next that I can try myself? Thanks in advance.