Mark – You did not specifically say what your stride rate is when running naturally. I am going to make the assumption that it is slower than the forced rate of 180/min. With that assumption in mind, do you notice your base of gait change when running at 180/min. (The base of gait is the side-to-side distance between your feet. If you ran such that both feet landed on a line drawn down the road, your base of gait would be 0.)
When you force your stride rate, you may be altering your gait. If you have weak hip flexors you may be using your gluteus maximus and tensor fasciae latae to initially pull and abduct (swing the leg out) and then use the adductors to pull and adduct (swing the leg back in). This type of motion will typically cause a reduced base of gait compared to a stride using a more vertical lift using the hip flexors. The reduced base of gait increases pronation.
The tensor fasciae latae and gluteus maximus both connect to the illiotibial band (IT band). So if your effort to quicken your stride is causing you to recruit these extra muscles, you are putting more strain on the IT band. Further, any increased pronation that results from a reduced base of gait will cause tibial rotation that will also act to increase IT band stress as the tibial rotation literally pulls the IT band around the lateral (outside) knee.
The other issues relative to when you are playing frisbee golf would be shoes and surface. IT band syndrome can be aggravated by shock transmission up the leg. Try running (not frisbee golf style) on the grass to see if that is the issue. If you are wearing different shoes, it could just be that your running shoes have a broken down midsole, allowing more pronation, and just need replaced. Last, consider shoe lacing. You can greatly increase the motion control of a shoe by snug lacing (as opposed to looser lacing). The issue is rearfoot control, which is the key to reducing pronation. You may just be subconsiously tightening up your shoes when you play frisbee golf, to get better stability for the start-stop action. If so, lace the shoes just as tight while running to get the motion control benefit.
There are a number of assumptions here, but hopefully you find some of this useful.