Sounds like a good quality line (LMR-400 or such). The better antenna cables are like that. Really long/high power/high frequency stuff is even more fun - more like plumbing than cable
The RG-whatever crap Radio Shack sells has losses that are unbeliveable, especially over 500mhz.
MN's down in the 150ish area, right? Pretty tolerant - when you get up near 500, little things mess it all up
I just did the antenna/cable replacement on a water tower (same one with the 19 foot antennas), two 80 foot runs. With an identical new antenna (same make/model, even), and a slightly better feedline (7/8ths inch Heliax vs 1/2 inch), we picked up 10 db.
How old are the repeaters in MN's system? I'd imagine they've been swapped out over the years. But then, I've seen remarkably old (read: vacuum tube) equipment in places - it just managed to survive through the upgrades.
Up around 900 Mhz, errant golf balls hitting feedlines have been known to wipe things out. I once fixed a broken system by just reterminating one end - the entire loss was through a damaged connector.