98 Dodge Truck with a attiude

I have a 1998 Dodge 2500 5.9 Diesel 12 valve with 145,000 miles when I accelerate after it has warmed up I will have the tach then the speed odomer and volt meter go out until I let up on the accelator also the oil pressre and gas gauge drop out and come back at different times I have been told that it was a problem with the computer so it was replaced it still did not correct the problem and was told it could be in th dash cluster this was also changed out and still did not fix the problem I found the alternator to be bad and changed it went through and checked and cleaned all conections and still having the same problem no one seems to know how to fix the problem this problem does not happen in cold conditions until the engine warms up to normal operating temp. I have been to 3 dealers and no one can can help me with this. :Cry: