1998 suburban tranny problem

Hi, any ideas or help on this problem will be appreciated. I've got a 98 chevy burb with about 132,000 miles. Wifey was driving it the other night, and the truck was driving fine on the freeway. Problem started when she got onto city streets: truck goes from 0 mph to about 30-35 mph finein OD , but than will not go any higher. I tried driving it and it seems like it will not shift into next gear, engine revs high and truck wont go any faster. If I ease off the gas it drops below 30mph and sounds fine. Any ideas? Please?

Couple questions.What is the colour and level of the oil in the tranny?Have you had the filter and oil changed during the 132,000 mile life of the tranny?I'm thinking that the filter maybe clogged and not enough oil to supply to the clutch packs.The same with a low oil level.Has the check engine lite come on?If so ,get that checked first.I hope this will help.
chuck's

Hi, the fluid is dark, when I checked the level, it looked like there wasnt any in it so I added to it to bring it up. I just changed the motor oil and filter myself about a month ago and it is still in acceptable levels. The color of the transmission fluid was a dark brown? I guess.... The check engine lite has not come on at all. I'm not sure about the filter for the transmission or the fluid being changed, I bought the car used. any ideas?

Scott

The tranny oil should be red.Turning brown indicates that the oil has been burnt.You may have internal tranny problems,but I would change the filter and oil and give that a try.Dropping the pan will also give a better indication of the tranny condition.Lots of fine metal pieces can indicate failure of the tranny.I don't like to give bad news but dropping the pan,checking for metal pieces,changing the filter and topping it back up would be a start.
chuck's