Trans flush

Is it really nescessary to flush a GA transmission at 100000 miles? They used to say that was a waste of money, just change fluid and filter.

flushing the trans is NOT a good idea at all.
It washes away friction material, and usually causes trans failure, basicly it causes it to slip which creates more troubles than its worth.

I'd just change the fluid and filter.

Change the fluid and filter only! Don't flush unless you are flush with money for a new transmission. High mileage transmissions are usually destroyed by flushing for the reasons Xeroinfinity stated.