Hi I just recently replaced my transmission in my 96 k1500 and it sputters and backfires now but it ran smooth before hand Any suggestions? I have to make a 500 mile trip soon and need to get it fixed please help!

 

Check to see if a vacuum hose or any electrical connection has been left unplugged or damaged.

 

There was one plug I could not find it was a long one that was square and had 4 prongs that went into it still can’t find it

 

That could be your problem.

 

is the connection to the plug clean? sometimes Gm's wire harness will have a plug for an accessory thats not used in every application. if the plug it clean then it was probably used if its dirty it might have been not used. make sure your grounds are all connected and clean and no wires are pinched between the trans bell housing and engine