i'm not sure what's causing that. Here's a link to an overflow valve, but I bet a new one was put in with your vp44 when you replaced it, (that and all new crush washers on the fittings)
Overflow Valve Dodge 5.9L 24V VP44
I was guessing it was losing it's prime due to a air leak. If you park downhill ... see if starts normally. I fit does, there is a air leak into the return fuel. usually it's the return line fitting (banjo bolt on at back of cylinder head) loose or leaking. They have those crush washers on them, and sometimes they leak. Any leak can cause hard starting.