sporatic surging during take-off

The problem i'm having with truck is surging during takeoff. When the truck is in park there is no surging. Once it is placed in gear the surging starts. Trans is not slipping, fluid is good and the filter has been changed, with no leaks. The truck is a 1990 gmc suburban 2500 4wd with a 350. Initially I thought it was the fuel pump. I have since replaced it 3 times, the last time with a pump for a 91. It was recommended because it was thought the the fuel pressure was low and the 91 pump has more pressure. The surging problem was there before the new pump and is still there after. I replaced the fuel filter when the pump was replaced. After this I thought it was a electrical problem. I then replaced the cap, rotor, wires, plugs, coil, map sensor, throttle position sensor, coolant temp sensor, and for good measure the egr valve. It has a new fuel pump relay. I noticed that it backfired through the throttle body, which could indicate timing problems. Looked and found out the timing chain needed to be replaced. New timing chain now. Finally because I hadn't spend enough money I replaced the two injectors. One common problem is that there is a fuse that will blow if the surging goes on long enough. It is the ECM-B fuse (10 amp). Looking at the wiring diagram this fuse goes to the fuel pump oil pressure switch, and the fuel pump relay. My question is if the oil pressure gauge is reading fine can the switch still be bad. Is this a common problem. As a point of note I swapped out the computer to see if that was it. Same problem was there. I'm sure this is a simple fix that i'm over-looking. I just cant put my finger on it. Oh yeah it came up with a Oxygen sensor code....well you know whats a couple of dollars at this point so its new also. Please help.