240 in generally good condition, 145k miles . No idea of service history - I have had the car for about 5k miles

On a long trip (in hot weather with lots of stop and go traffic) I noticed a slight lurch (and a slight change in transmission sound) when the gearbox was changing up at slow speed (<15mph). Most noticeable when changing up but not accelerating. On accel it seemed smoother.

then this week in about a 2 hour period heard maybe three lounder short dull 'clunks'- the first seemed to be coincident with going over a slight bump and braking hard - the other two were at random times, one at about 50mph another at 15mph.

In the next trip of about 5 miles, there was a strong burnt transmission fluid smell (fluid is brown, not dark red) - fluid clearly need changing. The level actually is at the high end of the scale when hot (can slight overfilling do any damage ?)

Wanted input on what to do in order to diagnose. I guess I was figuring on flushing and refilling the tranny as a first step and see what that does. Reading other posts here is sounds like worn engine mounts or tranny mounts might be a culprit ??

Any ideas or recommendations ?