HOLD ON THAR!!... If there was any real HP increase (supposedly due to increased air density), wouldn't it be there for the first few minutes after you started up cold, and then fade away as the engine warms up? I don't experience that, hence, I have to call partial BS. (OTOH, I'm going to continue to carry the 1/4" jumper ell, 5/8" coupler, super-duper tape, and other means of roadside coolant system repair.)
As for neglected coolant/systems, I let my factory fill go for 9 years (*blush*), but only 33K miles. (Didn't know about the factory grit--those FoMoCo bastiges, lol.) Coolant became black-ish, but not at all thick or syrupy... some of the black was visible particulates, which I assumed was decomposing hose rubber... yet old hoses (the MAIN BIG ones anyway) seem to have a nice smooth green staining from the anti-freeze... hmmm...
Anyway, did a couple tap (hard) water flushes--forward and reverse--in the driveway, until it ran/drained clear, then added Zerex Super Flush and topped off with tap water, with the OLD HOSES in place. I'm no chemist, but this Zerex brew must be milder than the stuff Wicked and other pros use, because you leave it in for 4-6 hours of RUN time, no limit on engine-off time.
Super Flush did the job (drove around for a week), "liberating" all sorts of additional "stuff" that dirtied the water (rust? hose rubber? scale?). Couple more fwd and rev flushes, ALL NEW HOSES, then fill with 50/50 DISTILLED H2O and plain old green PEAK. Burped by parking nose uphill, left corner slightly higher.
Will NEVER let it go more than 2-3 years again... promise!
Couple months later, still clean and green... fingers crossed.