jkier
Maybe the clunk is in the drive train,drive shaft.Check where it hooks to the engine and rear,past the flex disk on the rear.Maybe the roll pin has things wore out.
When the engine sounded stressed did you notice any difference in speed,I supose you would being you stated you were on a slight incline,but did it sound stressed on the flats and did you notice any speed changes then.
Yes check the fluid levels,How were they??Last time you did a filter change?? Last time you changed the fluid???Water in the fluid??
Just a few things I thought you might want to check........
Jason