Do the plug changes that No lift had said. If the ignition system is good it will have no problems with the colder plugs. I use a 125 shot of nitrous and when I had a 3500 stall convertor in it would stay at 5000 rpm all the way thru the run. But I ran 11;81 @ 112. I switched to a 3000 stall convertor and went the same time at 11.81 but went 114 mph. I also had put in a 2004r trans with a lockup convertor. you will get used to the high stall. The rpm does need to be up higher to get all the weight going. you will be ok with the 75 shot on the stock parts. Just keep an eye on the plugs and don't run too much timing. I would not go to 5500 if the engine would not do that on the cam you have. It will try to get there nitrous doesn't care about anything it just wants to go at all rpm ranges. hammer that baby with the shot and stay in it all the way I smell a high 12. I went 11.91 rolling into it like you did. Run a couple gallons of race gas when you run the nitrous. This will help with some of the detonation.