Cab Mounts or tracking arms?

['70GMCStep]

Got another question for you all. Ever since I bought my '65, I've noticed on right turns from a stop there is a bump or two like something is shifting a bit. I'm thinking cab mounts which should be here tomorrow. I did turn a left turn the other day in a parking lot and felt like I was riding a shopping cart with a bad wheel while turning left. Rear trailing arms? Here's what I do know:

I've been underneath it and looked for things. Found nothing. New CCP tubulars in front with new discs and spindles. Had my mechanic check my work, turned out well there. Been aligned, cruises down highway straight as a pin and stops just as straight. New heavy duty shocks on all fours, and been up and down the frame last summer grinding her down and painting it. No defects that I can see. What do you all think?

Thanks as always,
'70GMCStep

'65 Chevy C-10 lwb bbw
'70 GMC Stepside swb