fishy1

I hope someone here can help me out a little. I have a 2005 GMC Yukon Denali with the Vortec 6000 motor with 103k miles with an automatic tranny. Just recently, when shifting from first to second, the tach revs really high until I let off a bit and then it shifts pretty rough into second. I have tried to find a previous post about this particular vehicle but have not come up with anything. The tranny fluid level is good and does not smell burnt and still has a reddish color to it. Im thinking of changing the tranny fluid and filter to see if that helps. I have read some other posts about different vehicles with similar problems and it looks like it could be a bad sensor or TCM. If anyone has any ideas I am wide open to suggestions. Times are tough and Im trying to do whatever I can myself before I bring it to a shop. Thanks in advance for the help.