727 3rd gear feels more like a down shift

I only have experience with manual vbs that were factory vbs converted to manual through the use of a shift kit. They DEFINITELY still require the use of a kickdown, or at a minimum tying the linkage back on the transmission to ensure adequate line pressure and therefore holding power of the bands and clutches.

I have heard but cannot confirm that some aftermarket vbs do not require any linkage.

Without a kd linkage your trans would work but the shift points, when in D, would be very early......untill thd fwd clutch wears out from slipping. When this happens the powerflow in third is the same as first as the fwd clutch slips in third.

The precursor and warning sign of this happening is when the 2 to 3 shift starts to allow the rpm to flare during the shift.