Steering wheel not returning to same center

[av.8r]

Got an '88 Chevy V30 Dually, crew cab 4x4 w/ 454, 76k miles & no rust. Installed a 4" lift (4" blocks in rear, probably closer to 5" springs up front). Steering correction was the 3" Rough Country block between the knuckle and the steering arm. Sway bar correction was the 2" RC brackets.
Ever since I did this, my steering wheel does not always center in the same place. It seems to change when a higher-than-usual load is put on the system, usually close-to-full lock, slow, and helps to be reversing. When I then go straight down the road, the steering wheel will have changed from level or near to off by as much as 1/8th of a turn, or vice versa. Sometimes a smaller change, only 1/16 or 1/32 of a turn.
I can't see any obvious movement from the block, both arm-to-block or block-to-knuckle, although with all the grease on it I could be missing something if its slight enough. Thought maybe the front axle was moving slightly on the left spring plate, since the hole for the bolt was ovaled front-to-back. Scratched a line, observed it, no movement seen. Put a wrench to the steering box bolts, all are tight. No frame cracks to be seen.
Before I do the real nitty gritty tests, has anyone ever dealt with this or something similar? I've spent a while googling the issue and haven't found anything similar. Thanks