That is strange. Without seeing it in person, looks to me like a heat or chemical reaction. Is the plastic still rigid when you tap your knuckle on it? If it is, then it's heat caused. If it feels flimsy and not uniform, then that's a chemical cause. But four years in the sun and finally buckling makes no sense. What's the underside look like? Are the fins broken or deformed?
That is odd. I just tried bending my spare grill and can't really make it look like that. I think it would take a substantial amount of heat to deform it like that and would expect some heat damage visible on the paint itself.
Thanks for all the replies...I loosened it up and let it sit but it didn't really do anything....The plastic, origional, is still hard. It looks like a shrinky dink put in the oven.......I'm gonna run it by toyota tomorrow and see what they think....Its really bizzare...
Did you buy the truck new? If not then it could be an aftermarket grill and just OEM spec. I ran into that issue with my driver side mirror, you know the one some people have said shakes while driving? Anyway turns out it was a cheapo aftermarket POS. Just something you could look into before asking the dealership.