I thought it was my carb but i dont think it is. I have an 85' Blazer....i had a shop put in a 350 hd 4-bolt that i orderd. I put inheaders,new true dualexahust, new radiator....and befor we had riped out all the unnecessary vacuum and emissions. I got truck back it ran fine. I couldnt wait to brake it in. Guys told me to wait for 500miles befor i went to go rompin. Around 450 is when it started to sputter and buck at 50mph then 45mph,35mph,30mph,now 28mph. So, i tought the carb? Smelled lots of fuel....so off to the shop it went. Tought to do it myself but did some reading andWOW! All greek to me. Got it back from the shop he said "Runs great but took him a long time to dial it in and i didnt havethe proper bracket for the passing gearso i didnt have that"PASSING GEAR NO PROB! Drove off samef*#kin problem. PLease help!

 

Is it an automatic transmission and does it buck and sputter if you drive it in 2nd gear?
If it's ok in 2nd then it's probably a bad torque converter lock up switch and the wiring can be disconnected or replace the switch.

 

Yeah, TH-350 dont know if its the one with the lock up or not. The lock up sticks right out of the tranny...big plug thing..right? By the way it only does this when in drive andif i stay on the gas it dies.