Accelerator pedal cuts out as rpm builds

[tree98]

Ok so here's an update and a slight revision. This truck is a 2019 western star 4700 with a crane mounted to it. Has a Cummins L9 totally factory. The CEL comes on and to rev it up you have to hold the pedal down for about 5 seconds as the revs slowly build up. It runs normal and will rev up as high as normal, its just that lag time from an idle.
BUT..... as I said, it's a crane truck, so if you engage the pto and get in the cab of the crane (also a throttle pedal in there) everything works fine, engine revs as normal. The tps's are the same so I switched them thinking maybe the one in the truck cab was bad, it isn't it works fine in the crane cab. Any ideas? I haven't been able to get a code out of it, I'm waiting for an insite update.