6L80 Tuning 1st Gear Downshift issue

Got an extremely heavy 2014 1500 Suburban with a 6L80, was doing a tune so it downshifts at set speeds to engine brake as I live in the mountains and have to follow alot of slow vehicles up and down. Every gear works fine except for first, it will downshift into first but there is no engine braking it just coasts until you touch the throttle then the RPMs rise and it acts like it should until you let off again or until it coasts fast enough to get into 2nd.

If you put the gear selector in M and put it in first (only in first gear locked does it work) it acts like I want it to, but it won't do it in drive. Is that just how these transmissions are or did I do something wrong/miss something? I set it to downshift to first at any throttle position at 16mph which is 1mph under the 2nd gear upshift for under 69% throttle.

Everything else seems to work like I want it to but first gear trying to coast without throttle. Otherwise I'm very happy with my setup. Thanks!