1994 Ford F150 Econoline transmission problem
 

I have a 1994 Ford F150 Econoline van 5.8L 107,000 miles. I believe it has the 40D?? transmission. When I drive the van it revs and sounds nice from 0-30, at about 35-40 miles per hour, at this speed the engine dose not rev but the van shakes, stumbles like 3 to 4 time (bucks) (lags out) then at 45-50 it drives fine again. The trans fluid is a light red, do not know when the fluid or trans filter were changed last.
I think the transmission needs a flush, new filter, and a new torque converter. To make the van run well again but the shop said the transmission needs a full rebuild at 1,700$$$ and there's nothing else they can do for the shifting problem. I can get a Jasper rebuilt transmission for 2,000$$$ installed from a garage. The garage wont change the filter or the transmission fluid or install a torque converter without installing a new transmission. They say its not worth it. I am going to get the jasper transmission when i need it.
I was wondering what i can do to make the transmission shift better??? Lucus transmission slippage oil?? or murrys transmission fuild??? I have never used any transmision slippage fuild before so IDK..
Thanks for reading, any ideas, thoughts, or suggestions greatly appreciated!
P.S. I been driving the van like this for the past 6 months, lol. I put 7,000 miles on the van in that time. Paid 600.00 bucks for the van. :)

From the symptoms you describe, an engine problem can also produce results like you are seeing.
Many times spark plug replacement helps. If you have not had anything done to the engine it might be a better place to start. Things like spark plugs, wires, cap, rotor are routine maintenance items and either one of them if defective could also produce those symptoms , and cost less than a trans replacement. If you cannot do the work get a few estimates first. 107,000 miles is not a lot on those engines. They did require a little regular maintenance and ran well if done.

Sorry for no back info.
Let me start. I did the spark plugs, wires, distributor cap, rotor, radiator, upper and lower rad. hoses, heater core, heater core hoses, serpentine belt, idler pulley, belt tentioner, front and rear brakes. i think that's it so far......600 dollar van to a 1,000 dollar one real fast. lol, at least i know whats new.
There's no check engine light on, and it turns on and off when you start the van. so i am at a lost. i have not tried to scan it or use that plug or single plug yet. trying to learn how to do that.
I swear the sound and lag is the trans. or mainly the torqe converter clunking 3 or 4 times then working. i wish it had a tach to monitor motor.