Initial Transmission Lag

I have a 2002 GMC 2500 Sierra 3/4 ton with 6L and Auto transmission. It shifts normally into reverse, but takes too long to shift into drive. I was told by my local mechanic that it might be something to do with the 1-2 shift soleniod or the 2-3 shift soleniod. These are expensive to replace, especially if it does no solve the problem. I'm just wondering if anyone else has had any luck fixing a similar problem. The oil and filters were all changed, therefore I think it must either br mechanical or electronic.
Thanks, Woodstock

was the problem there before oil and filter change if not not sure if applies to your vehicle but on some gmc's seal at filter has a tendancy to move when replacing filter and causes oil to cavitate or not get sucked up properly sucks air and causes shifting problems

[I can check that, but yes, the problem was there before. I bought the truck knowing that it was in a roll-over, but had both my body-man, and mechanic look it over, both giving it the thumbs-up. I figured even if the tranny goes, it was such a good deal, I'd still be way ahead and I couldn't pass it up! The lag is the main reason I changed all the fluids when I bought it. Nothing had metal in it and everything smelled normal. It doesn't seem to affect performance, it's just annoying and I'd like to clear it up!
Thanks for the reply, woodstock.