Trans 1999 Venture

1999 Venture extended van - Thursday the van started to lunge every time the transaxle would shift. There is also a whirring sound coming from below the vehicle while the van is moving between gears. I drove it about 2 miles once it started and parked it in my garage and left it there since. The fluid looks red, clear, full and clean. There is no obvious odor to the fluid. I have approximately 59,000 miles on the van. There is a history of a cracked exhaust manifold gasket which was replaced around 40,000 miles. No other major repairs. The outside temperature was about 95 degrees and the van was operating at the normal temperature. Does this sound like a new trans is likely or could there be some components that should be checked before a trans is suggested? What should I expect from my mechanic? Are there any trans problems known concerning GM minivans?