Hi Bob,
It is a problem with the shift point retard- causal chain.
The way it works is, that the HFM-Box operates a solenoid vacuum switchover valve (2-prong black box). In cold engine conditions it lets manifold vacuum (black vac. hose) through to the AT- control cable vac. canister. That sitts on the right side of the AT and is connected with the s/o valve by the green vac. hose. In the canister the vacuum alters the load information coming from the ctrl. cable, so that you get a late up-shift when the engine is cold.
Test the system by evacuating the control cable canister through the green vac. hose first. If it's holding vacuum, ensure that you get manifold vac. through the black hose. Then evacuate the yellow check valve distributors. Test the s/o valve by evacuating and actuating while the connector is off. Use +/- Batt.
All the best,
Dokta