99 grandprix stumbles under load.. (new issues)

sorry for starting a new thread..
same car. has new issues. well sorta.. =)

so..

the car stumbles and damn near dies as soon as you put it in gears
drives horribly
but revs fine in park or nuetral..

weve changed the transmission
the egr, mass airflow censor, fuel filter,
the code we are getting is still the same p0753
tranmission solinoid (cant spell sorry)

the same code with both transmissions
so im assuming the trans is not the problem

we,ve checked the hoses for leaks found nothing

i am so stuck right now.. and i have to work tommorrow!!!!!! lol
so help is urgently needed..

thanx in advance!!!:banghead:

Normally I would not allow a new thread on similar issues or ones that you have already addressed to the forum but I'll let it slide this time. However, just so we cut down on confusion and redundant answers here is the previous history at link below.

Click here (http://www.automotiveforums.com/vbulletin/showthread.php?t=913510)

ok update...
just changed the ignition module and coil
changed throttle posistion censor
and still the same issue

fine in park and nuetral
when i shift down into park.. you dont see the effect right away
until.... i take my foot off the brake
the right back to the trouble.. i dont even have to gas it

Suggest two things.

1. check the IAC motor (idle air bypass around the throttle blade), and more specifically the port which it meters...could be coked up due to PCV flows and not getting proper idle airflow, especially to compensate for the additional load of the torque converter working against a set of locked up clutch packs. The IAC should be able to compensate for the load in "D"rive before the throttle is cracked off the rest position.

2. check fuel pressure. Again you could be marginal enough on fuel pressure to run the engine against no-load...throttle "blips" don't use much fuel. But once into a load...again against the torque converter working against a locked up clutch pack that's ultimately restrained by the brakes. Could be a fuel pump itself.

3. Pinch off the vac line which leads to the vacuum brake booster...if there's any problem with the booster it could lead to a massive vacuum leak (unmetered air not compensated by fuel in order to maintain the desired A/F ratio). In general look for any other possibilites of vacuum leaks...a smaller possibility, as usually those would constitute an inability to idle in the first place.