I have a couple silverados with a couple different questions. first. i have a 1994 z71. it has lost almost all power. and ive exhausted all options i can think of. all new sensors ecm injectors. fuel filter. pump. vacuum lines. everything. the only thing left in my mind could be the cat. the truck has a 5.7 with i believe all the smog pump stuff removed. not too sure of the history but i got it with 150k on it. it now has about 350k. i think it might be clogged because the guy who had it said he never replaced it. and i never have. so maybe that might be the problem. also once it gets hot i hear a dull roar from right where it is under the cab. so im thinking it backed up so much it found another route out. onto my 1988 silverado which i just purchased about 15 minutes prior to this post. i paid 700 for it so its not too bad. its got a six cylinder in it. which i dont know the size. on the drive home. i noticed a bad tap in the motor. which was not there at the beginning. not a big problem i pressume. probably a lifter loose. or a valve tap. not sure. but i hope its nothing major. truck has alot of power for the motor. so im sure its not extreme. im just wondering if its common for that motor for the studs to walk out because i had a previous truck where the studs backed out on me. couple more questions but nothing major. it has a leak at the collector. im guessing blown gasket. but like i said it has enough power for me not to be super worried. just wondering what the tap could be. with putting my ear close i can hear its coming from the top of the motor somewhere. the crank and everything feel tight. and it doesnt have any dead pistons. everythings firing. thank you. sorry for the run ons.