95 Eclipse with 99 engine

Ok, I hope someone can help me. I have a 99 engine in a 95 eclipse. A month getting the engine installed, I start losing power. I had the spark plugs changed and the oil changed but still the same problem. In the low rpm's (below 2500) my car sputters and pops if I press too hard on the accelerator. This results in my sluggishly easing up my speed which can be annoying for me and other drivers on the highway. Plus, once up to speed the car still can't perform and was the engine settles in the lower rpm's, it's difficult to pick up speed. Please help.

Checked for boost leaks??

Welcome to AF. Please put the year, model and tranny in your sig.

yeah, need a little more info there. 4g63? 420a? mods?