Thanks for the ideas guys, I found out there were 2 things going on with this delay - the inline filter was plugged up so I cleaned it, but I still had a bit of a delay from time to time after that.
I think it relates to how hot the water gets. When I have my heat setting to the hottest position on my truckmount, the water gets over 240 degrees and with that heat built up, it seems to put a lot of pressure on the trigger in the wand. I'm only running it at 400 psi when this happens.
As soon as I turn the heat down and it gets to 225 - 235 degrees, the issue goes away. Not exactly sure what's happening inside the wand to relieve whatever pressure there is when it's overly hot, but I think that solved it!