90 Suburban 4x4 transmission not shifting right

Hi,
Am in need of help bad. I have a 1990 Chevy Suburban 1500 4 x 4 w/350 engine and 3 speed overdrive automatic transmission. We just use it to get lots of groceries or haul stuff from Menards home or pull the boat to the lake. the last few times it seemed funny about shifting from 1 to 2nd it would shift alitttle higher rpm or speed a few times but not real bad just seemed a bit off. Today we took off for to go about 1 and half hour drive to do some shopping and it seemed a little worse about shifting up to 2nd but the other shifts seemed ok. As the day went on it got worse and then started to affect the 2-3 shift and this evening on the way home it never shifted into overdrive. I checked to see if it had a vacuum modulator but did not see one. I checked the TV cable and is not broke that I can tell as seems is hooked up to something still. Fluid level is ok and not burnt smelling. We were going to go to the lake tomorrow first thing so I am hoping it is something simple to fix.