94sleeperZ

Ok, just to give you a little background it’s a 94 Z with 83,000 babied miles, I am the second owner and the first was a grandmother school teacher. I have had the car since last year and only put about 500 miles on it or so. The car is in storage right now for the winter and we plan on taking it to Florida this year. It has a SLP loudmouth 1, Hypertech chip (not the programmer) and I just put on a K&N FIP kit and did the TB bypass. After I did that I started it up (like a do every week) let the car run for awhile and snapped the throttle sounded great. Once the car got warm I did the same thing and it fell on its face, shook bad and back fired. I even held it at about 2 grand snapped it and it fell on its face?? But when I bring the revs up slowly it does fine?? Any ideas??? I kept the opti covered up, no antifreeze got on it. Also last year I replaced the thermostat (180) because it was sticking. My car gets all the way up by the orange hot line before the fans kick on?? Is that normal?? When the car fell it was right in the middle on the temp gauge. Is in the fuel pump, opti??
Cody