After having my transmission fluid changed with my 90,000 mile servicing, my automatic transmission began shifting
improperly. Often it will rev up before surging into 2nd gear and seems generally sluggish. A mechanic friend suggested I have it flushed to remove any particles the fluid change left, but this hasn't helped.

Any suggestions?

try taken it to the dealership and have their mechanics take a look

the throttle cable from the tranny to the throttle body needs to be adjusted. the factory manuals shows this. very small and precise measurements...