DOC Car Question: 1991 Mercedes 500SL issue

DOC Car Question: 1991 Mercedes 500SL issue

I have an issue with a 1991 500SL that has been difficult to troubleshoot.  Maybe someone is familiar with this issue on the R129 model and knows the solution.

Facts:

• Car was found parked outside for 5 years.  It did not run when it was picked up.
• Both fuel pumps were replaced along with a new fuel filter.
• Oil and coolant flushed.
• Gas Tank drained
• Car passed smog
• When the gas pedal is pressed gradually, the car will accelerate and change gears with no problem.  If I stomp on the gas pedal to the floor and hold it there, the engine will rev but the car will not go any faster than the current speed.
• I suspected the gas pedal kick down switch which was replaced along with the kick down solenoid on the transmisison.  No effect.
• The engine computer was swapped out with 2 other computers and still the same issue.

What is the problem?  How to fix?