1995 Toyota Camry Vibrating wheel and transmission fluid co

1995 Toyota Camry 4 cyl Front Wheel Drive 99,432 miles

My Toyota Camry's steering wheel vibrates when I accelerate to and above 35 mph. I also notice that the car is very slow/resistant to increasing speed and a strong burnt rubber smell is evident. I recently had the transmission fluid changed due to the black color of the fluid. The mechanic told me this was due to the fluid burning and not being replaced when it should have been. He flushed out the old fluid, replaced it and said that this procedure may cause problems to the transmission which may need to be replced with a rebuilt one. I was told that the cost would be around $1,500 and if I took it to the Toyota Dealer it could cost as much as $4,000 (for a new one I assume!). The mechanic test drove my car but did not notice any problems. Please help me.