Is it possible to use so much coolant system stop leak that you could clog the transmission cooling system?
The fluid is burned and seems like I am having problems with gear shifting and power from the transmission.
While the transmission line does run through the radiator, the transmission fluid does not mix with the antifreeze/coolant. (unless there is a major internal leak, very bad) If you have used a lot of stop leak I am assuming you have a coolant leak or overheat. I am also assuming you are only putting the stop leak in the radiator. The overheating could have overheated the transmission fluid, (or the tranny could have it’s own set of problems). Burned fluid should be drained and fresh fluid put in. If you are very lucky this may solve the problem, but I would not bet on this. Having problems getting power from the tranny sounds like slipping, do not drive the car this way, this will ruin the tranny if it is not already ruined. Give your local shop a call to have them tow the car over for a work over.