clutch/tranny

[Chevyguy]

Sounds like you are getting some firewall flex, and the clutch is not totally dis-engaging every time you shift.

There are firewall stabilizer kits, or you can fab up some support plates if you are gifted that way.

The throwout bearing can bind on the bearing retainer. The Aluminum retainers can develop grooves where the throwout rides. Switching to a steel retainer can cure this.

Problems with the alignment of the trans and /or bellhousing esp if an aftermarket bellhousing was used can also cause binding of the throwout bearing. The center of the bellhousing hole has to be in line with the crank centerline.

Problems with the clutch fork or pivot ball can cause binding.

I still think it's an overly stiff clutch causing firewall flex, and incomplete disengagment