not firing out of pas side of engine

Hi i have a 1997 GMC savana 5.7l 350 vorteck that has a problem, when you first start it it runs fine until you put it in gear than it sputters and runs like crap until it warms up, well we thought it was the cats so we cut them off and put a piece of flex pipe in place well one day both of them fell off 1 side of the pipes well i thought it was only 1 of them so i put the 1 back on and started it and i heard the other pipe blarin so i took it for a drive and all of a sudden the pipe that was blarin was quiet and it was running like crap than i let my foot off the gas and the pipe was blarin again and so i hit the gas again and the pipe was quiet again so i think that the passenger side of the motor is not working under load and i have no idea what i could be any ideas would be great..

p.s. we changed the spider fuel injectors to the new kind that are not supposed to varnish up, changed the fuel filter, looked at the distributor cap and rotor and it looked fine, changed the upstream drivers o2 sensor.

so i found out the problem well the radiator had a small pin hole leak witch sprayed onto the computer and made it short out witch made it not fire out of the passenger side of the engine