Dgyfrsh02

I've been Keeping an eye on the temp and it never goes above 200( highway and city). Thats not too high, is it?

I have a 2003 Silverado 5.3V8 Z71 LS Automatic. 119K, and still on 1st Tranny(Amazing, I know). So, during the summer is the only time I have a problem with the transmission. Slams from 1st into 2nd gear upon take-off(esspecially goin uphill), Then check engine light comes on and it keeps me in 4th gear. Only during the summer though(Southern New England)? Had some one diagnose it but they couldnt figure it out because it happens randomly and throw like 5 different tranny codes. In contrast, It's ideal in winter, 4wd works great, no problems plowing snow out of my lot. Any Ideas????