Dont give up yet you may just need valve adjustment. The exhaust valves on the v6 will tighten up after 70k or so and then that cylinder will start getting lower and lower compression eventually leading to a misfire and then if you continue too operate it it may burn that valve.On my v6 with about 120k miles i had several valves that were way to tight and a slight misfire starting to become obvious.When I did a compression test I found 2 cylinders with pretty low compression -I then pulled intake and valve covers and checked valve clearences and sure enough 4 of the 6 exhaust valves were too tight and the tightest ones were the cylinders with lowest compression. After changing shims to bring clearences into spec all my compression readings were then fine and truck ran great. This is a very commmon problem on all 3vze v6s -almost all will need exhaust valve reshimming when they get up around 100k or more.I pulled my cams out to do the job which made access to shims pretty easy -you measure (or may be able to read stamping) of all shims on too tight valves and then order thinner ones which will bring clearence into specs -probably need fsm for this job. Good luck, Bob.
