Does your check engine light function.
If it is connected and not on I would go with the stuff you mentioned.
There is a cylinder balance test the can be run with a handheld tester, might depend on year. The other thing is the cats, if they are old. I use a handheld heat sensor to check if they are hotter than the exhaust pipes.

My 245 will clunk going into overdrive. I lessened the clunk by adjusting the shift points a little. I think this happens because the Volvo's are lower geared and the AOD shifts at a lower speed than in a ford. I think the fords are at like 2.73 or something verses the Volvo 3.31, 3.91...

For the 5.0 there is always the Mustang forums to check too.