very slow acceleration

i have a 1994 3.2l rodeo 4x4 with the automatic transmission. I recently had bith headgaskets done, and the heads rebuilt at the same time. i also had to put in a new ignition module and six new fuel injectors. now the engine seems to run fine at idle, but stumbles when you press on the accelerator, when im driving it has very slow acceleration, and sometimes backfires when it gets to around 4000 rpm, it also stumbles on the way there. the mechanic who did all the work says that the timing belt is lined up, and fuel pressure is perfect, i changed the oil, and went a little heavier for the first 500km ( 15W40).
i was wondering if the transmission fluid could be causing some of this slow acceleration as the vehicle has sat for a while ( since late january), and it also seems to have an exhaust leak around one of the y pipes, before the cat(could uneen backpressure affect like this?). the only other thing i can think of is that when i was running it trying to figure out what was wrong a lot of gas got into the exhaust( it was running out the tailpipe), could this have maybe done something to the 02 sensor or the cat?
Also it makes a funny metallic noise under heavy acceleration, that seems to fade when you let of the gas but comes back when you hit it again.
anyone who can offer any ideas or help would be greatly appreciated.
thanks,
Dave.

I would start with a compression test just to make sure the valve timing is set properly. Something plugged in the exhaust (plugged cat) will also cause sloooow excelleration. Is the check engine light lit?
G/luck
Joel

nope, the check engine light is not lit

I'm not sure how it's done, but there is a way exhaust shops can test for excessive back pressure in the exhaust system. Could be something to try.
G/luck
Joel

thanks. i will look into it.
it now seems to be doing something a little different, it will accelerate to about 2000 rpm sluggishly, then will drop right down to about 1500rpm, then seconds later its right back up to where it started?:banghead:
I was wondering if there could be somethin to do with the transmission trying to shift, or something strange.?
any ideas?

just to clarify, it only seems to stumble badly like that when its wet or raining. i put new wires on, and no difference?
any ideas are appreciated
thanks. dave

ive got a 93 rodeo 3.2 same problem idles great but wont accelerate hardly replaced fuel tank pump filter all fuel lines alt plugs wires all sensors no codes timing is at 10 degrees idle not sure what it should be hope to get it figured out ran good once then hit some waterholes then started acting up again been sitting for days to dry dont help

I wonder if both of you have a clogged cat convertor.

CanadianRanger - you mentioned a metallic sound, how many miles are on your rig, and have you ever had to change out your timing belt and timing belt tensioner?

actually checked the converter on my when i first got it and it was hollow i was told that it may be a ground problem im still looking:confused:

igot mine fixed took the plenium off and cleaned and tested the injectors and had one sticking put it back together with some silicone on the gaskets and havent had any problems took it through some flood waters almost three feet deep and lots of mud