After years of stalled progress, I'm finally getting my project vehicle going. So far it's mostly going well, but I'm having a problem. It starts & runs mostly just fine. The problem arises when I'm coming up to a stop. If I gradually brake and roll up to the stop, everything works fine. But if I brake hard, it has a tendency to stall.

It's a mild AMC 401 V8 with an RV cam connected to a 700R4 transmission. I have the lockup torque converter working as it would in a factory GM car, with the vacuum switch and brake switch in place. So the lockup torque converter is unlocking properly. It's set to an idle speed of around 600 RPM and it will occasionally drop below that. Sometimes it catches itself and surges a little (which can be disconcerting when you don't expect it). But sometimes it will stall out. It restarts just fine. Part of the problem is that the handheld controller is basically dead. The LCD screen is shot and it doesn't appear to be working at all. So I can't monitor the system or change any settings. Is there any way to get just the replacement handheld or do I need to just eat the cost of getting a computer & handheld (554-116)?