stagnating rpm on my 348?

I have been shaking down my 1990 348 during the last couple of weeks since I brought from the LAX area, running it up to 5-6000+rpms while accelerating [never over 7000 rpm] and it has been running like a clock.
This shakedown has been going on for the last 600 miles and at high speeds
on DFW freeways and slow speed within all reasonable speed limits in urban areas. Absolutely running like a clock.
Then this afternoon [Wednesday 29th, June] at around 55 mph and 3200 rpm and in 3rd gear, I experienced what I thought was a momentary rpm stagnation when I stepped on it a bit it just did not accelerate much rpm whatsoever. I did not downshift to second since I definitely noticed an rpm stagnation at basically 3,000 rpm. I thought it was me so I ran it up again and it performed fine. Then I decided to check it again and entered the freeway and just like abovementioned, the rpm stagnated at 3000 rpm at around 50-60 mph in third gear and was definitely able to identify the problem. Quite a lot of accelerator pedal travel and it acted stagnated and then would kick in back to normal.

Again, all of the sudden the problem disappeared and the thing went back to running like always like a rocket. At 55 on third, step on the gas and the rpm just jumped up normally with terrific acceleration. The engine runs terrific and idles at 1,000 rpm like clockwork. Going to see the boys ar Norwood tomorrow to have it checked.
It seems as some sort of pedal to engine electronic fuel control microswitch, or the fuel control unit itself? of some sort. Would appreciate any opinions guesses or technical advice which might help although I am sure that the guys at Norwood will figure it out.
Thanks
Manny
ps
Hi Mike K:
I hope you read this since it will be the write up and I hope you can find it and fix without too much trouble. Sound like another microswitch to me.
I hope so.

 

Hi NoDoubt, Bill and Ken:
had it checked out this morning by the Norwood guys in Dallas.
Not a peep on the diagnostics box.
It was probaly a loose electron probably within one of the TPS [Throttle Position Sensor] and right now it is not showing any discrepancies in the diagnostics box anywhere and thus back to driving the hell out of it and have great fun with it. Drove it back home at max smash and rpm throughout all ranges of the spectrum on LBJ and it was just an animal!! It ran fabulous and not a sneeze.
The super guys at Norwood told me to keep an eye on it and eventually more electrons will trigger a good diagnosis but for now just have fun and take good notes in case it does it again.
thanks for telling me what your ideas were nevertheless.
Take care
MM.
nice cars you guys have there!!