My car is has been having a stumbling problem the past few days. While driving the car stumbles at 3200 rpm, and then clears out after about 3500 rpms. It also does this the whole time when you floor it. It almost sounds like its lean poping in the exhaust.I did notice the engine trys to throw more boost at it when it stumbles. When it first started I was at a stop light and noticed the rpms going up and down about a 100 rpms. After doing this at the stop light it hasnt done it since then. The car does not do this while its in park it revs up fine, it has to be under a load. I checked the resistance in the coil packs they checked out good, and I checked the plug wires. I replaced the spark plugs last may, I havnt looked at them yet but im guessing there fine, there autolite iridium plugs. I replaced the fuel filter a few months back, not that a filter would cause a problem this bad.The car has a L67 with about 115000 miles on it, so its expected that things are going to start to go out in it. Any help on this would be much appreciated thankyou!!!!