Cascadia electrical problems

I work for a small repair shop and we've got 2 Cascadias with some serious electrical problems here that we've about run out of ideas on.

First is a 2009 Cascadia DD15. Customer claims the accelerator pedal was replaced within the last month and just started acting up. I've verified his complaint that the truck will idle perfectly fine but as soon as you give the pedal any pressure the truck drops 50 rpm and starts lope-ing as if 3 cylinders have been cutout. The really weird part is that if I wait 15 minutes or so and start the truck, I can get maybe 15 seconds of the pedal working perfectly. We've gone through all the basics of checking battery/ground connections, cleaning ecm plugs, and double checking the correct type of pedal is selected in the parameters in DDL8. We've swapped pedals with another truck here as well but it still acts up within 15 seconds.

Second truck is a 2012 Cascadia DD15. Has a low voltage problem. Batteries, battery connector cables, alternator, and starter are all new. Alternator puts out the correct voltage. Batteries are charging from the alternator. New starter engages correctly. I personally installed the starter. Everything else was done just before the truck came to us (within a week). I've checked that the connections are all tight and clean of major corrosion. The alternator sense fuse blows the instant the truck starts. The dashboard battery light is on and the message center says "warning low voltage." We replaced the voltmeter and the connector wiring behind the instrument cluster. It looks like someone has been doing electrical work before us on this truck and could have cooked something somewhere but none the modules (mcm, cpc, sam, acm) are reporting any problems. Literally only codes that comes up in DDL8 and JPro are for low voltage being reported by the mcm and cpc.

Any help would be very much appreciated cause I am stumped and have exhausted all the obvious basics.