Pto/blower/cruise problems

morning everyone,

Been having an intermitten issue with my 98 pete 379 with 60series 12.7 detroit. I haul cement and when im blowing off i use the cruise control to rais up the rpms to 1300 to run the blower. Latly ive been dealing with the cruise randomly shutting off while pumping. Sometimes if i take the tractor parking breaks on/off a few times then it will stay on no problem, other times i have to push the clutch pedal in/out a few times for it to stay, other times if i move the truck an couple inches forward/back itll work. And other times it will stay on with out an issue for weeks.
And what confuses me is when it decides that it dosent want to stay on it will run for a couple mins then cut out but if i disconect the pto or run the blower with the hose disconected it will stay on untill i start to open the product valves on the tank then it will cut out.
When this happens i revert to a screwdriver wedged under the dash pishing on the pedal but when i put the load of the blower on the rpms drop to 800-900rpms which then makes a 45-50min pump time into a 2hour pump off.

Any ideas?

 

Hmmm... could be. I unplugged the speedo because the gauge would read 80 when i was doing 10mph. But its been like that for some time now

 

Rustybolt, it could be. There is not 1 specific thing that makes it work again, sometimes playing with the clutch works other times the brake pedal other times its the parking brake. Im thinking bout just replacing all the sensors that tie into that system just to be safe lol. The cruis cuts off when im running and the jake cuts out also but i verified that is a result of a intermittent clutch sensor.
The clucth does not shut the cruis off when im in a high idol however

 

How did you diagnose that? Scaned with a computer??