Fuel pump issues show MORE with load not less, NOT the fuel pump..........he says clearly it runs fine higher up. BUUUUTT..............you can possibly check by filling tank up past 1/2 way. When pump goes bad the problems show up at low levels of fuel, say under 1/4 tank, for sure at 1/8.
OP should question what all he did, should've been improvement there not worse, meaning something later done wrong. First place I'd start is TPS-is car an automatic? If so they sold the wrong TPS for it................as the correct one is not available. Manual trans TPS absolutely will not work on ATX, even if it seems to bolt right up.
Next? How the IAC sealed to intake, was old seal removed, what was used to seal this time? They have a tremendous propensity for sticking the wrong gasket in the IAC boxes it seems.
Don't be afraid to look at your own work critically, it's one of the best tools you have. Unfortunately many absolutely cannot do that. Why they get rid of perfectly fixable vehicles.