transmission

my friends transmission on her 02 GT is shifting hard. Sometimes, even if not on the gas hard it won't shift from first to second until between 5000 and 6000 rpm. The fluid level is fine and it doesn't smell or appear to be burnt. Any ideas on the problem? I know something about engines but not a LOT about trannies. the fluid and filter was changed about 20,000 miles ago and it JUST started happening. Thanks

could be a clog'd valve body or a bad pressure control seloniod

Any codes? (max adapt code set) EPC's go bad alot in those

haven't checked for codes. Will do soon.