Loss of torque during hard WOT downshift

[740iLIndividual]

Just bought an '01 740i Sport, 105k miles, and it has an issue with acceleration. No issues moving the gear selector into R or D or P (cold or warm) and the transmission shifts and launches well. With normal driving up to about 2500rpm, no problems. If I drop the throttle to accelerate, it acts like someone stomped the parking brake as the engine is trying to rev. The revs climb but the speed does not match, but it does slowing accelerate. Could it be torque converter, valve body, TCM, other? The previous owner had fluid/filter changed about 4k miles ago and 'just drove it gently' to avoid the slipping. I think the issue was occurring before the fluid change. It did shift properly with no shutter or banging.

Please advise with any history of similar issues.

[740iLIndividual]

A few more comments:
No P codes were set. No 'Fail safe' warnings shown. It seems to drag the worst around a 25-30 mph downshift and hard acceleration. No rpm hunting during normal driving.
I recently drove about 100 miles at 70+ on the interstate. With a 5->4 downshift up long hills, it also seemed to drag. I'm guessing the 3000 stall speed on the Sport TC ties in with the expected speed of the dragging.

[asianvenom]

This is symptom of a bad valve body on a 5hp30, but 5hp24 is not know for bad valve body...? Or could it?

[740iSport303]

This is symptom of a bad valve body on a 5hp30, but 5hp24 is not know for bad valve body...? Or could it?

Actually, 5HP24 also has valve body issues. There was an updated valve body issued by ZF too.

[Timm]

If you have slipping clutches then you should have the TRANS FAIL-SAFE PROG message and gearbox codes set. If it were a clutch slipping I would expect the revs to go to 5500 RPM and bounce off the rev-limiter. To me this sounds more like and engine performance problem, and this behaviour is often associated with a failing MAF. Try a run with the MAF disconnected and see if that makes any difference.

Another possibility is partially blocked cats - although that often throws engine codes.

[asianvenom]

If you have slipping clutches then you should have the TRANS FAIL-SAFE PROG message and gearbox codes set. If it were a clutch slipping I would expect the revs to go to 5500 RPM and bounce off the rev-limiter. To me this sounds more like and engine performance problem, and this behaviour is often associated with a failing MAF. Try a run with the MAF disconnected and see if that makes any difference.

Another possibility is partially blocked cats - although that often throws engine codes.

Good point here...