Stalling problem after T5 swap

I have a 89 LX convertible and 2 weeks ago and had the AOD T5 swap performed by a reputable shop. Everything is great, but I have noticed one issue. When I downshift and use the engine to assist in braking to slow the car down to a stop, as soon as I push the clutch in (and hit the brake) the RPM drop and the car stalls. Now if I do not downshift to slow down to a stop and use only the brakes its fine. Also, if I’m quick enough and blip the throttle right before I stop (like in heal-toe shifting) it won’t stall.

I’m baffled. The idle is fine, set about 600 RPM and does not surge. I have no modification, heck it still has the air box silencer. Any ideas??

Thanks,
Pete

Thanks for the reply. I have a feeling that it might be the VSS. The auto computer should be fine. This does not have to get swapped out.