Acceleration Problem
 

Here is the issue I am trying to figure out. It has happened twice so not consistently. I have a 04 Ranger 4.0 4x4, automatic, 250K miles. when driving at speeds 50-60 mph, I let off the gas for a bit to remain a safe distance from another car. As I accelerate again I get no power. The RPM go up like I am reeving the engine, but once again absolutely no power. I pull to the side of the road to a stop and put it in park then back in drive still all RPM no power.
It is like it is not engaging
So I drop it into second and BOOM I'm moving again. After this I get back into drive and everything is fine.
Any ideas of what this issue could be? Fuel? Transmission?

Welcome to the forum

Its the transmission, for sure.

Is there something specific, no not really, but best guess is that a solenoid is sticking when you are coasting, this releases pressure in the system, as it should when coasting
I will get worse over time
Check fluid level and look at the color and smell

All automatic transmissions run on fluid pressure, that's what engages the clutches and bands(brakes), fluid pressure
The solenoids(electric valves) in the valve body route this pressure to engage the bands and clutches to place trans in each gear
If a solenoid's valve sticks then that pressure is lost for the other solenoids so no gear can be selected, so feels like neutral

Best bet would be to take it to a transmission shop and have them do a pressure test, there are ports on the side of the transmission where the pressure inside the transmission can be observed while transmission is engaged

I would imagine you could solve the issue with a newer valve body with solenoids, and you don't have to remove transmission to do that
But at 250k, assuming no previous trans rebuilds, the bands and clutches will be worn, doing the valve body only is not a waste of money since that is/should be done on a full rebuild in any case

If you decide on a full rebuild, its VERY important to get new Ford Pump, must be Ford, a new one-way clutch and OverDrive drum, a soft parts only(clutches and bands) rebuild will guarantee trans will be back at the shop in 12-18months
And always a new torque converter

And any time a transmission is off on any engine, you should replace the rear main seal on the engine, its a cheap part, $10, but hard to get to if it starts to leak

Interesting. Thank you for the input. The transmission has no previous rebuilds.

So after getting pressure tested you are saying a good first step you be a new valve body/gasket?

I don't think as of now I want to do a full rebuild but I'll have to think on that.

After pressure test you will know more, that's when you decide what to do

If new valve body I would also install shift kit many found this to be a good upgrade

You have a 5R55E transmission