95 Turbo runs like crap

[95MitsEclipse]

Alright i got a 95 eclipse gst that decided to throw a piston through the block awhile back so then I got a local shop to help me out due to not having ne time to do it myself he ended up puttin a 93 motor in it, running 15 psi, and basically everything else being stock it ran when i picked it up, but would run funny at times like it would boost but it didn't take off like it wanted to but it just didn't, decided to check some things out, pulled all spark plugs, all turned out to be white, no carbon at all on them, check compressino all cylinders were 150.....now i have no clue why my car decideds to run good at times and then at other times just sit there and let the turbo spool, also only got 120 to the tank as compared to the 200 before the diff motor something def wrong any help???

 

[Bostedquest]

the MPG drop alone suggests O2 be checked/changed...

 

[95MitsEclipse]

U really can't check O2 sensors can u??? its basically hit or miss with them Ive been told