87 300e transmission woes

[momentum]

My 87 300e tends to stick in gear at speeds above 40 mph. When is sticks the rpms go up and I have to give it more gas untill it shifts to the next gear. My tech told me over the phone that It just might need a filter and flud change. Can a fluid / filter change bring things back to normal or do you think I should start looking for a rebuilt one. If so what's the average price for a rebuilt one? Car has 149,000 miles on it.