transmission fourth gear?

[smartin]

1985 300TDT (125K miles) At first, accelleration from zero very sluggish, with 3 "hesitations" until about 35 mph. Since then have cleaned ALDA line, diesel purge direct to IP, adjusted ALDA, changed return (diesel) lines, thermostat ( was'nt hitting 80 degrees), capped vac lines to EGR and recirc valve. The ALDA and recirc valve made the most noticeable difference. (I also changed the 2 fuel filters twice - once about 4 months ago, and after purge last week.) Car is a lot quicker from zero, but still has mini "hesitations" (versus before when they were a little longer causing car to "lurch forward" a little) I did notice that if I start in "L", and then shift upwards, finally to "D", - only a hint of these hesitations. Finally on the freeway the car feels like it is working a little too hard - revving 2500 PLUS at 55 to 60 mph. Is it shifting into fourth gear? There - I took long enough to get to my main question - but thought maybe they were related. I just received trans filter and gasket - (plan to do this weekend) Although earlier posts suggested I have a good mechanic do it the first time.