47-59 Help! Transmission acting up?

[Chopped53]

I'm hoping one of you truck gurus can help me troubleshoot my problem.

I've got a a '53 Chev with a crate 350 and 4L65E automatic transmission "connect and cruise" package from Chevy Performance. We installed everything about three years ago and have put on about 8000 trouble-free miles since then.

Until now.

Been doing a lot of highway driving lately and it's been hot (at least for Canada). This weekend I drove a hour or two north of the city for a show, then the next day drove a couple hours south for another show.

On the way home last night, cruising along in top gear at 2100 RPM (65 mph), the transmission just quit pulling. I popped it into neutral and coasted along until I could pull over. Then, I shut off the engine, put the car in park and checked it out. No visible problems, no funny smells, fluid levels all clean and good.

Got back in the truck and it wouldn't start. Had to get it towed home.

It did a similar thing earlier in the day as I was leaving the show. I was in first gear just pulling out and the transmission seemed to disengage. I pulled over, put it in park, then back into drive and it seemed fine again.

What do you think? I think it might be something electronic. Maybe the transmission "black box" is acting up? Also, I'm thinking my neutral safety switch might be faulty.

Any insight from the forum members would be much appreciated.

Thanks.