8 Speed Shift Issues, ONLY when bed is loaded

[DENALIHD66]

This is a bit hard to describe but I'll try my best.  I have ALWAYS had sloppy shifting in my 2015 6.2L with 8 speed.  But when I have a heavy load in the bed (500+lbs) I experience a really odd shifting behavior.  When I am shifting from Drive to Reverse (come to a full stop) and I let off the brake, the truck starts to drift backwards, as if its engages, but then it starts to buck several times, followed by a clunk roughly 2-3 seconds after starting to drift backwards.  Unloaded, the D to R shift typically is fine.  But when I get enough weight in the bed, it just behaves so differently.  

 

Now, when I'm under the truck on flat ground and truck is off and in park, my driveshaft is tight and has absolutely zero play in it.  All my strength cannot make it move whatsoever.  When the truck has weight in the back, correct me if I'm wrong, but essentially the driveshaft would be slightly more horizontal and changes the angle of it.  When it becomes more horizontal, is it then putting extra pressure on the transmission trying to shift normally because the driveshaft is now "longer" due to the weight in the bed?  This is the only thing I can think of.  I want to clarify that this happens when I come to a full stop AND when I shift from D to R before coming to an absolute complete stop.  

[DENALIHD66]

Anyone have any input whatsoever?

[JimCost2014]

On 4/8/2021 at 5:23 PM, DENALIHD66 said:

Anyone have any input whatsoever?

Try using the Tow/Haul feature on the transmission to see if it makes difference on the driving portion, not sure why it is rolling back in gear. Could just be the weight and miles on the truck.

Edited April 11, 2021 by JimCost2014

[DENALIHD66]

7 hours ago, JimCost2014 said:

Try using the Tow/Haul feature on the transmission to see if it makes on the driving portion, not sure why it is rolling back in gear. Could just be the weight and miles on the truck.

Same thing happens in tow/haul mode too.  Again its hard to describe, but its an occurrence that ONLY happens when I stop, shift it from Drive to Reverse, truck starts to drift backwards (as if reverse is engaged) but then that's when it starts to buck for a second or two until it makes connection.  Just really odd and I'm trying to figure out why