Shift solenoids limp mode? HELP
 

2001 ZR2. Trans shifts good in all gears. Does not slip in any gear. I have a trans cooler on it. Here's the problem. On hot days or on real long drives the trans starts to act up. Running along at 60 or so and starting up a big hill it wants to kick down a gear from 4th to 3rd but won't. As it slows it feels like I'm in 2nd gear. Once over the hill it shifts up to high gear again and all is well until the next hill. I can stop and let it cool down for maybe a half hour and it runs good again. Is the trans going into limp mode. Could it be the shift solenoids? HELP!

if you dont have a external transmission cooler might be worth a try. ive seen the built in coolers in the radiator get clogged before causing transmissions to go all screwy.