Is the thud when doing a kickdown (opening the throttle), or while coasting down (at closed throttle)? And do you know specifically which shift is giving you the thud (5-4 or 4-3)?
Regarding the "slip," often people will notice the torque converter clutch (TCC) engaging, just after a shift into Overdrive. So you get an upshift, and then maybe a second later the engine speed drops another 200 RPM or so. Some folks think they are feeling the trans "slipping" during the shift, but in reality it is two separate events: the upshift, followed by the TCC engagement. So if this is what you're feeling, it's probably normal. You could have a dealer tech ride with you (with a scan tool, displaying current gear and TCC state) to confirm that this is what you're feeling.
For that matter, having a tech ride with you (with scan tool) would be good for diagnosing the thud, since that would let us nail down exactly which shift you are getting the thud on. They can also make recordings of the bad shifts (using the scan tool) so we can see exactly what's going on. Have them record current gear, target gear, TCC state, engine speed, turbine speed, output speed, line pressure, desired line pressure, throttle angle, and the OD, 2C, 4C, and UD pressure switch states. Dealers can then upload their recordings to Chrysler, and I can look at them. If you go this route, post your VIN (last 8 digits) here so I can find your recordings.
Regarding the "slip," often people will notice the torque converter clutch (TCC) engaging, just after a shift into Overdrive. So you get an upshift, and then maybe a second later the engine speed drops another 200 RPM or so. Some folks think they are feeling the trans "slipping" during the shift, but in reality it is two separate events: the upshift, followed by the TCC engagement. So if this is what you're feeling, it's probably normal. You could have a dealer tech ride with you (with a scan tool, displaying current gear and TCC state) to confirm that this is what you're feeling.
For that matter, having a tech ride with you (with scan tool) would be good for diagnosing the thud, since that would let us nail down exactly which shift you are getting the thud on. They can also make recordings of the bad shifts (using the scan tool) so we can see exactly what's going on. Have them record current gear, target gear, TCC state, engine speed, turbine speed, output speed, line pressure, desired line pressure, throttle angle, and the OD, 2C, 4C, and UD pressure switch states. Dealers can then upload their recordings to Chrysler, and I can look at them. If you go this route, post your VIN (last 8 digits) here so I can find your recordings.