When your driving down the road at 55 mph it will slow down like its got no power. The speed will reduce from 55 to 25 and it feels like it is going to stall out. In the meantime,I have my foot on the accelerator.

Take to a transmission shop, likely you need overhaul or replacement.

I would give it a tune up, plugs wires. Mostly under a load will it miss eratic. I would start there. Im sure youll find thats what the problem is. As far as trans, do see that happening.

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_a3369546f8067589

check if the fuel filter needs replacing

you need to scan the computer that has a electronic throttle body and a electronic gas pedal one sensor goes bad and the system goes into limp mode

Sounds like the solenoid is going in the transmission, typically it works or it doesn't though.. In a similar case, I had several strands of the power wire were broken.
Problem is many people are too scared to look too deep into it and transmission repair shops like to pay their mortgages for performing this type of work...
Otherwise, simple things which may have been overlooked -- have you (properly) checked the transmission fluid? Some cars require to run or turn off the vehicle or even run through the gears before checking the fluid level... so be sure you have the correct way of checking the fluid level in your vehicle.
Ck

The EGR valve is unserviceable which causes a bad or insufficient fuel control for em-missions......Hope this helps you out........EGR valves are not very expensive.

The following drive cycle can be used as a guide to assist with re-setting monitors when a vehicle specific drive cycle cannot be located. This OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F and the coolant and air temperature sensors within 11 degrees of one another). This condition can be achieved by allowing the vehicle to "sit" overnight, and then by beginning the drive cycle the next day. Most drive cycles will be difficult to follow exactly under normal driving conditions, so the driver should exercise caution, road safety, and courtesy to others.

1. . Start the engine. Idle the engine in drive for two and a half minutes with the A/C and rear defroster on.
2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle.
3. Hold at a steady speed of 55 mph for three minutes.
4. Decelerate (coast down) to 20 mph without braking or depressing the clutch.
5. Accelerate back to 55 to 60 mph at ¾ throttle.
6. Hold at a steady speed of 55 to 60 mph for five minutes.
7. Decelerate (coast down) to a stop without braking.

ball joint
control arm
shocks
brake rotor
and all your suspension parts have them check by your mechanic