2001 Mitsubishi Eclipse hard start and stumbles under load

Engine Performance problem
2001 Mitsubishi Eclipse 6 cyl Front Wheel Drive Automatic 137xxx miles

i got a 2001 eclipse gt on my hands that ran "great" then got engine detailed. The car is now in my shop, cranks like a champ, then generally fires right up the third time cranking. I have checked all things needed for a engine to run, its getting air, the fuel pressure is at 50 psi running, gets sparks, and the compression is about 135. Once the car is running idles a bit off, but under load car falls on its face almost to the point of stalling. I have even dropped the Y pipe in assumption the cat's where clogged but that changed nothing. I've racked my brains nearly to the point of walkin out of this shop! Please help any assistance would be great!