When I was flashing my tp to cricket, i had to install an old 1x prl for my area and then do *228 and it would update my prl to current. Had to always do it that way. I don't know the flashing process to get mpcs but i'm sure there was a method in it that required a particular prl to be installed to work. It was the same with cricket, but the required prl was outdated. So I found a way around it that worked for me. Try some test and find the prl page that has all prls. Will see If I can find the link and edit this post.
http://www.corolada.com/prl/
The way i found the 1x prl that worked for me was by installing it and dialing *228. If i had the wrong plr, it would go halfway thru the ota programing and hang up. Also when I had the current prl update on my device, the *228 ota update would go half way then hang up. Like I stated, I don't know how mpcs works, but it was my cricket experiance. Try some testing and see what works.