What would cause random voltage spikes to around 17 volts? on 1990 Chevrolet 1500 Pickup

I am getting about a 17v voltage spike during the first 10-15 minutes after start up. They will hold for a few minutes then drop, and return again. After the engine warms up, they seem to go away.

Any thoughts as to the cause?

Asked by for the 1990 Chevrolet 1500 Pickup
alternator. repair it before it damages your computer

Thanks! I was thinking this or voltage regulator...
2 more answers
take your alt in to a auto parts store to be checked if its good then it could be your voltage regulator
1990 Chevy 1500 4.3 V6 Kept having to get a jump to start it so I replaced the battery and after a few days it started needing a jump again to start it so I took the positive off the battery while the truck was running to see if it was the alternator and the truck stayed running with the positive off the battery so I said it can't be the alternator and just yesterday I got a jump and right after the truck died after about 5 minutes of running and now it won't start back up I don't have a lot of money to replace this part or that part The truck sounds like it's dead when you try to start it and after 3 times of trying to start it It has no juice in the battery Can someone help me with this problem I'm a woman and know a little about motors and has to fix it myself just don't have money to replace parts that are not the problem