1988 Nissan Sentra Initially car stalling and surging at 40

I had no mechanical problems before I put "seafoam" in crankcase and gas tank as a recommendation from discount Auto in Rockport Texas. After 5 miles after putting the sea foam in my car it begin to surge (cut out) at 40-45 miles per hour. When coming to a full stop it stalled. Starts fine, but stalls after starting. As long as I kept my foot on the gas pedal it would not stall. After warming up it would not stall at a light or when stopped.

Went to Midas on a refferal (by the way she is an excellant manager and excellant mediator in Victoria Texas) Her tech put BG into fuel tank and said put supreme fuel in tank and run it hard. I did fill it up with spreme gas and ran it to about a little more than a 1/2 of tank. It did not improve nor worsen the situation (same symptoms) and I thought I better just go to Nissan. Nothing against midas.

I took it to the Nissan dealership with these same symptoms. I requested a fuel injection cleaning first. They replaced mass airflow sensor and throttle body position sensor without prior approval or permission by the way. Inj cleaning cut was paid for but appears to be some discrepancy in whether it was done or not. Basically they say if we did it on the OR we did it. Their OR says it was not done, but my receipt states an InJ cleaner kit was purchased no description of injector cleaning or condition on ticket.

Picked up car. Next morning when I tried to start the car, I had to turn car over approximately 5 to 7 times. Also had extremely rough idle. Returned car to Nissan. They increased the idle 50 rpms above specs and replaced a blown fuse. The car started not as good as it did before I brought it in, but it did start and the idle had improved but was not inconsistant.

Did not drive the car much and can be verified by odometer reading. The service manager and customer service rep stated the car was safe to drive and I was able to drive to Colorado. Packed my car ready to travel 900 miles. When putting in reverse it sounded like it was going to stall. It did not stall, but when entering highway speed of 50 -55 miles per hour it begin to surge as before, loosing power, picked up again, begin to loose power down to 30 miles per hour on highway. At lower speeds 40 and 35 miles per hour it lost power to 15 miles per hour and I had to continue pumping the gas pedal to keep it at 15 miles per hour. I made it back to Nissan dealership.

* NOTE* The owner has stated we have spent many hours for free diagnosing this problem it will cost you $2 - $3000 dollars to fix your car, we do not know what the problem is, but on Monday I will have the tech complete the diagnosis and tell you the final cost to you and see if you agree to it?

Currently tech states fuel pressure is fine, fuel pump is fine, injectors are working properly, ignition coil fine possible ignition system or replacement of computer?

First I need to know my rights are and second what is your diagnosis based on the initial systems and the repairs that were made and its current condition which is worse than before I started?

Be happy to provide a donation if you can help resolve this situation satisfactorily.

Best regards.