Need some auto allstars' to help me with my 94 Buick Century!!!?

Specs: 94 buick century; 3100 v6- M eng code; 120,000 miles; no previous problem! current problem is when the car is in a drive or reverse gear, and I press the accelerator the voltage and temp gauges start to climb into the red extremes and the dash lights pop on, but if you hold the rev long enough everything will snap back to normal and then repeat. the problem started over a year ago, was advised to change ecm, after i changed it the problem went away folr approx. 6 mths, recently started again so I tried another ecm, but it's obviously not the problem. any advice or previous experience with this would be great! this really has me stumped. the car starts and runs superb jus this intermittent problem any help would be greatly appreciated!!! __________ Thanks in advance!