The engine rpm's increase and decrease when in

Without a general description of what the noice sounds like, squeal as compared to knocking, it is impossible to help you. Engines make a lot of different noises, so try and help by describing noise. I would suspect it is belt related, or tension pulley related as these are RPM variable noises, belts tend to slip when you accelerate and can be quite loud with a serpentine belt as example.
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Is the car equipped with the Automatic Transmission?
If so, read on.
Otherwise skip to the end and answer some questions.

POSSIBLE SCENARIO:
I have observed a condition where my car surges slightly when the torque-converter clutch (TCC) cycles between lock and unlock when driving on an uphill grade.
First some basics and history that will explain why the TCC is used.

Engine, Torque Converter, TCC, and Transmission relationship--
The TCC allows for a solid connection between the engine and transmission which allows the input to the transmission to rotate at the same speed as the engine.
Without a TCC, there is slippage between the engine and automatic transmission. The slippage is greatest at low engine RPM. That is what allows the engine to run with the automatic transmission in gear, like when you first shift into gear or stop at a stop sign. When the throttle pedal is depressed, the engine RPM begins to increase and the torque converter begins to slip less and less the more the engine RPM increases. The car moves. But even at cruising speeds the torque converter slips slightly. Engine RPM is greater than transmission input RPM, which is realized as slight decrease in fuel efficiency.
When acceleration is complete and a constant speed is being maintained, the engine power output is reduced to the point where the TCC can engage and eliminate any slippage between the engine and transmission. If the car has a tachometer the engagement of the TCC can be verified when a slight reduction in engine RPM observed without a corresponding change in vehicle speed.
One method used to test the operation of the TCC is as follows:
Find a flat section of road where it is safe to perform the test.
Reach a steady speed and keep the gas pedal depressed with one foot. While observing the tachometer (or listening for an increase in engine RPM), with the other foot depress the brake pedal enough to activate the break light switch but not enough to engage the brakes. When the brake light switch activates, the TCC receives a signal to disengage. With the gas pedal being held steady, release the brake pedal and the engine RPM should decrease when the TCC engages.
Old cars with Automatic Transmissions did not use a TCC. I believe the TCC was put in use in an attempt to increase fuel economy.

MY EXPERIENCE WITH SIMILAR SYMPTOMS
The condition that causes that issue on my car is this:
- A slight uphill grade increases the load on the engine.
The car tends to gradually slow and it is necessary to depress the gas pedal to maintain speed.
- Depressing the throttle pedal (manually, or automatically with cruise control engaged) signals the torque converter clutch to unlock when the load increases slightly. (A more drastic load increase would signal the Transmission to downshift to a lower gear.) The corresponding increase in engine RPM and output is enough to compensate for the reduction in speed. When the vehicle speed, engine RPM, and throttle position stabilize to the point that the TCC will engage and the engine RPM will reduce in correspondence with TCC engagement. Now, if the road conditions have not changed, power output is not enough to maintain vehicle speed. With the increased load caused by full engagement between engine and transmission, and the cycle (surging) repeats itself until the road conditions change.

Does that help?
If not:

QUESTIONS
Please define the symptoms.
What are the road conditions when the surge occurs? (A slight uphill grade?)
What is the frequency of the surge?
Does the engine power output have a noticeable surge?
Is there a speed change related to the surge?
Does the tachometer move up and down with little or no change in vehicle speed?
Are all instrument indication in the normal range?
What else has changed?

Good luck!

I would consider changing the vehicle speed sensor. When they go bad, they can really throw out a lot of bad data to the computer, resulting in unexpected behavior like you're experiencing. They're only around $20-$25. I hope this helps! :)

did they install a aftermarket or dealer alternator ran in to this exact thing on a focus dealer part fixed it

Check first the fluid. If you need to add or you may need to replace it. Other than that it could be some dirt or debris internally on the gear valves or it may be a bad torque converter.

Try checking your timing to solve the ping problem, your timing might be too far advanced. For the downshifting problem, I have this same issue on my odyssey, On the top of your efi manifold you will see 2 wires that control your throttle, One of them extends to the transmission and basically lets it know when you are pressing firmly on your gas pedal, telling it to downshift. I would adjust it so the cable has some more slack in it, therefore requiring a harder press on the pedal before downshift, and hopefully a sooner upshift. You can also slightly adjust idling problems if the van is running high while in park or drive while sitting. As for the gas vapor purge code, I would first try replacing the egr valve, its only a couple bucks and takes no more than 5 minutes.

check the engine breather pipe if its split or perished it will cause this ,if its ok then its a new idle control valve or it may just need a clean

you could be low on transmission fluid check that and make sure it registering properly on the dipstick.

Yes most likely, the brake switch also sends power to a solenoid to unlock the shift lever. If the trans works fine once you get it out of park, the trans itself is fine

Check all your fuses and run a code checker at Auto zone to see if any trouble codes are detected if not the shift lever release solinoid is in need of replacing or servicing.