[Overdrive]

I really think we're talking about two different problems here, because I cannot see how any sort of problem with the radiators or their fans could cause what may be backfiring at high rpms from what you're describing.

Did your bumper make contact with the ground during this pothole hit you mentioned? If so, though there are protective covers under the car, maybe the radiator and/or fan was damaged in that way. Even if the fan is moving it doesn't mean it's working properly, and if one of your radiators is not functioning properly it's certainly possible for the car to get hotter than normal. The early cars had just barely enough cooling capacity through the use of those two radiators, and these cars do not stay cool when sitting still or when your airflow is blocked by traffic in front of you.

If you want to actually be sure that they're both working, run the car, turn on the air conditioner (this forces the fans to run) and then get out and put your hand under the bumper in front of each front tire. There is an opening where the air exhausts straight down to the ground in front of the wheels, and you will definitely feel the air on your hand if they're working.

As for the other issue, it sounds like you're describing your car as an automatic. Is that correct? If so, then I would have to ask if you have tried to see if the phenomenon happens at those high rpms when you shift the gears yourself when you're in manual mode?

Are there any warning lights on in the instrument cluster?

Best thing to do, honestly, unless you don't have another mode of transportation, is to park the car until you can have it looked at and worked on so you don't run the risk of causing more damage and costing yourself more money.