This is just Fords way of reducing power (rpms) when oil / coolant temp rises. Sounds like it was working perfectly.

Heres a couple of tables out of a max rev limiter section on a 6.2L strategy.

oil temp - rpms max allowed
400f- 4499
300f- 4500
200f- 5000
100f- 5550
under 100f- 5850

coolant temp-rpms max allowed
297 - 4499
293 - 4500
287- 5000
284- 5500
280- 5850