1996 blazer...replaced the spider 1500 miles ago. new ac plugs, new wires, cap& rotor, the whole shebang. engine has 156,000 on it. It ran great until my Daughter stopped at the store. When she restarted it, there was no problem until she got up to 55 mph. She called me and said the tachometer was fluttering. normally the tach is at 17-1800 rpms at 55. it was now fluttering around 2000-2200rpms. and the engine has a noticeable misfire. it idols great. no miss at the pipe. and no misfire in passing gear, or under heavy acceleration. when in park, and i slowley bring the rpms up at the throttle body, it has a misfire about 1800-2000.i put a scanner on it, and got a PO300, random misfire,which you are all aware of, no other codes. am i looking at bad plug wires?..they dont lightup with the water test..but even though they are new....they are a generic brand from a local "FleetFarm" store. the $26.99 special. one other thing i did was check for vacuum leaks, and found the MAP senser on the intake was leaking. the orange rubber was cracked so i replaced it. the weird part is, is i inadvertingly forgot to plug it in after a phone call, and of course the light came on...but the engine ran way better...almost 95% of the miss was gone. but it has a dead spot from a standing start, and is a little sluggish, but not a whole lot of miss. when i plug it in, it goes back to the misfire game. If any of this rings a bell, I would greatly appreciate some input and direction...Thanks.