Yeah, the 7700 really doesn't like to be geared. It is much more sensitive to gearing than the lower kv motors. Try a smaller pinion. If the 13T is still giving you high temps, then go to a 10T and try that. You might also want to see if you can get a bigger spur, although a 90T spur sounds pretty big already. Then go to tires, smaller diameter that is. If you can't come to a happy medium, then you'll have no choice but to go to a lower kv motor. Personally, I like the 4600. You can really "tune" performance with the battery choice on that motor. Everything from very mild on 6 nimh cells to uber wild and crazy fast on 4S lipo.