voltage regulator in 1989 3.9 V-6

[davemc53]

Am having a charging problem. No, not credit card!!! Anyway, the battery charges just fine when truck is sitting in the driveway, but when I drive to work, it is dead when I get there. I usually leave it running for 10-15 minutes, so that it will be charged when I go home.
I posted this once several months ago, and was told to replace the alternator, because the voltage regulator is in the computer. What if it is the VR, though? Is there a way to bypass it?
When it does turn over, the starter seems to work very hard when the engine is hot, and turn smoothly when the engine is cold. Could this have anything to do with it?
Also, I posted before that the rear end is making a "whining" noise only when moving, even when coasting with the clutch in. It doesn't seem to be a problem with the transmission.
How difficult and expensive is it to change the computer?
I'll take any help or suggestions I can get. Thanks.