I am having a problem with an automatic transmission in my 02 Silverado Z71 Ext.Cab Shortbed when I am shifting from 2nd to 3rd. Under normal to light acceleration the truck will stay in 2nd a bit longer than I feel it should, lets out a little squeel, and then shifts into 3rd. This only happens between 2nd and 3rd and it is more pronounced when I accelerate in Tow/Haul. I recently had the tranny serviced and had a power flush done on it. There are 66000 miles on it. Does anyone have any ideas?

On another note, during acceleration I am noticing some pinging. This has only started to happen within the last 2000-3000 miles. I am using 87 octane so I feel that shouldn't be a problem. Any suggestions?

I basically want some information that I can go to the dealer with. I still have my GM Major Guard Warranty for another 8000 miles or end of July. I would appreciate any feedback.