2015 5.3 6L80 no forward, reverse only

[Michael James]

After accelerating in sand up hill my traction control light kicked on, I attempted to override by pushing the TC button and lost all forward motion immediately. 
Reverse engages and I can also lock 4wd in reverse however no forward gear or forward movement at all. 
i dropped the transmission plate with no metal shavings and oil looked normal. Next I changed the separator plate with new check balls in the valve body. New filter and fluid with same result…any suggestions I’d appreciate. Not once did I hear any grinding and no codes were given on the dash. All shops want to buy a new transmission rather than trouble shooting. Please help.