E40D stalls in 1st gear

[sputnik801]

So - sometimes while visiting a friend who lives on a hilly dirt road, I'd put my 97 in 1st while going downhill. It was easier for the trans to hold the speed instead of applying the brakes and sometimes skidding a bit of loose gravel. Never had an issue before.
Now, if the truck goes more than 10mph in low, she stalls. I can restart it right away.
I had some work done in March to the valve body and had the convertor replaced. I have yet to ask the tranny place about this.

Anybody else have this happen??