Ford Super Duty (1999-2016) :: Low A/C Pressures While Being Over Capacity

In all fairness, this isn't for my SD, but there aren't really any forums for my '94 Villager and all A/C systems work pretty close to the same, so I thought I'd at least throw my question up here and see what comes of it. It's a bit of a hodge podge of manufacturers (Mercury, Nissan, Ford, Mitsubishi), but it's a Mercury, so technically a Ford.....ish.

My A/C crapped out last summer, so I finally got around to rebuilding it earlier this summer. I replaced absolutely everything except the rear expansion valves and the evaporators, which I flushed out with A/C flush and compressed air real good. Then I blew a line on a dirt road because I didn't get a line all the way clipped in. I got a bit paranoid about grit in the line, so I went ahead and replaced the line and dropped in a new dryer, sucked it all out good again, put a splash of POG oil in there, and filled it up with 134a.

According to the specs I could find, the capacity of my system is 52oz, or 4.3 of the standard 12oz cans. I always bleed the lines between cans to rid the lines of air and moisture as much as I can, so 4.5 cans usually gets about 52oz in the system. Anyways, it was 90 outside, so my readings should be 45-55 and 250-270. After adding 4.5 cans, and letting it run for a bit, my readings were still a bit low and my vent temp was only 60, so I went ahead and finished off the can. They were still reading low, so I sorta reluctantly hooked up another can and started filling. It sucked the whole can right up any my readings were 45 over 220 with vent temp at about 57. The low side is about on the low end of the acceptable range, but the high side still isn't quite up to the desired range and I don't want to stick another can in even though my readings indicate I'm not over-filled. I'm wondering if something's not right in there, or if maybe I'm just expecting too much from a 23 year old A/C design...?

Strolling into work today at 35-45 mph, it was a touch over 80 outside and my vent temp was a smudge over 40, so I guess that's not too bad. My radiator fans works fine, but they don't move a bunch of air. I usually drop an additional ~15 degrees when I'm on the move as opposed to sitting at idle.