1998 Sable LS 3.0 Duretec Engine Help!

I swapped engines so I get no codes. Once warmed up the car idles but when put in gear with the brake on - it sputters and dies. Moving it from neutral to drive without brakes - it will go forward and not die (sort of). Once the brake is applied while in gear - it dies. How can I diagnose without codes? Can I put it on blocks and run it in gear - will that give me codes?

There may be a vacuum leak in the brake booster that is causing the trouble. There most likely won’t be any codes for that kind of trouble unless the O2 sensor detects a leaner mixture.