Transmission 1-2 shift weird

[NeedsHelp]

Well I actually set this up for my friend. But his truck shifts weird from 1-2. He says that it kind of hesitates or vibrates a little between gears. This only happens when you are just driving around. It doesnt do it when he is at WOT or when he has the tow setting on. It actually shifts harder with the tow setting on and it doesnt do the weird shift. It is a 1999 Silverado 1500 Ext, Cab 2wd, v8(not sure which one). He has heard that its a problem with a spring in the valve body. But the source he found that out from wasnt totally convincing so I dunno. What do you al lthink, what could be the cause and better yet would is the fix??? Thanx

[Import Hater]

There's a TSB for this. I call it a shudder, but I think it says "judder" or some other wierd word in it. For me, it happens more on warmer days, engine/trans warmed up, and light throttle condition. The fix is an update to the alternator sense circuit.

 

Rob