Slipping is when the engine rpm races and the car goes nowhere.
The problem you describe is the transmission going into limp (failsafe, if you can call it that) mode. The ECU no longer controls shifting at this point. Line pressures are increased and this causes the hard shifting, the jerks while upshiting that you mention. Driving along like this too long will cause more problems. 4th gear will not engage and your torque converter clutches will slip, causing excessive heat buildup, frying the fluid and the rest of your transmission.
The CD4E transmission is very sensitive to maintenance, or the lack of... I suggest that you read the CD4E FAQ.
I recommend a transmission flush as a first step.
If this does not work, second step would be installation of a transmission cooler.
I highly recommend a rebuilt valve body using Sonnax valves and a TransGo CD4E jr shift kit. The only problem here is that this may accentuate other existing problems, such as a failing torque converter. If your transmission is not too far gone, the valve body upgrade will prevent more damage.
