90 gmc sierra runs like shi*?

[Stan]

it spun a bearing and i fixed it but the thing shakes and sputters like the timing is off but it starts fine an idles fine but when you drive it, its shit.when im driving and switch gears the truck slows down and sputters then speeds up then sam thing but after its warm it sputters any way.

the engine was also smokeing cause it got to hot abd i was sweating standing near it.

maybe the thermostat is stuck on that one but what about the sutter?

 

[Shirley]

sounds like its really cooked

 

[Mike V]

first thing I would do is check all vacuum and electric connections to see if you left something loose or off. then the thermostat. it's usually cheap and easy to fix.
if the truck slows when you let off the gas to shift, something is causing a drag. bad clutch or bearing? is the shaking possibly coming from the clutch?
if the engine speed drops more than it should and it runs rough, it could be because it's running too hot. or back to loose connection. you got detective work to do

 

[RacingFan]

if the truck slows when you let off the gas to shift, something is causing a drag.

Could the parking brake be on, causing both the drag and stutter?

 

[jdgreen]

this may sound dumb but the coolant temperature sensor plays a big part in how the truck runs. i changed about $300 in parts on my truck and it was the coolant temp sensor. the reason that it messes with so much is because it may be reading at say -20 degrees and making it dump in too much fuel. that could be the reason that it gets worse as it warms up. the cts is only $10 or so. i would try it before you rip apart that engine again. well hope i helped a bit hope you figure it out soon and cheaply.

Brent