It turns over but sound like there is no compresion

You did put 134a back in? But possibly not enough? There is a pressure safety switch somewhere in the system that detects pressure and opens the circuit if not enough freon. At least that is where I would start. Does the Compressor turn freely otherwise by hand? Did you get enough compressor oil into the system (new Compressors need special charge with compressor oil).

check that the cam shaft is turning over. ( broken timing belt / chain). If broken then the head will have to come off to replace the bent valves . If you have not done a belt before then get a workshop manual before you start or have an accredited mechanic do the job.

Have you confirmed that you are getting fuel into the combustion chamber. If this is a carburetor model, the needle might be stuck against the seat in the float chamber, especially if the new motor has been standing for sum time.

First you need to check your a/c clutch. This is located in front of your compreser, You can check by having someone ture on a/c and watch the compreser and see if it kick's in and turns, If it does your ok if not needs replaced, But more then likely you just need to charge you a/c unit with frezon. Best of luck to you.

check cylinder compresions,sounds like there low(worn rings)by the way the 5.7iroc is one of the worlds best engines.....

check them all. if they are the same then the engine is ok. If one is 15% lower than the rest the engine will stumble.

Time to find a fresh engine as it sounds as if this one is about toast. Not sure if you can find a used engine in a wrecking yard that is any better. There are specialized engine rebuilding firms that sell completely re-manufactured engines, but the overall expense might justify looking for another vehicle. Good luck!

i would get a compresion check .because it sounds like the head gasket is too thick, lowering the compresion would give the same results.but as its a simple check its the cheapest way to start.....

crank shaft sensor? I've had these be bad in a couple of vehicles, and I spent weeks/months worrying about the possible cause. Just a possible thought.

check ur slave cycl. sound like it failed