[ykdave]

Idle should be at 800rpm in gear with the AC on.

These things do not like a low idle at all. It will cause the hard starts unless you give it throttle and will cause the stalling you describe.

CumminsDatabase.com :: 12V Idle Adjust

Also, the voltmeter fluctuating is the grid heaters cycling, they draw almost 200amps which the alternator cannot keep up with while they are on!

 

[ykdave]

The solenoids RARELY are an issue. The boots may break up and cause some dirt to enter it and jam it up but thats an easy fix. also check the solenoid rod length.

The solenoid has 2 coils. One to hold pull up the rod which is energized when the starter is engaged. another coil holds the rod up and is energized with the key on. Usually the only way the solenoid burns up is when the starter contacts stick and cause the high amp pull coil to be energized for a long time.

CumminsDatabase.com :: Fuel Shutdown Solenoid

Get your idle speed fixed first though, its way to low.