Does anyone have a clue as to what would cause my Trooper to lose power at exactly 47mph every time?

It happens while accelerating up through the gears normally, all is well until it hits 47 and the engine loses power slightly until it gets to 48 and then all is well again. It does not misfire or stall, its as if I let off the accelerator momentarily, I am clueless as to what the cause may be. It may not be related but I go through an ignition module about every 1 and a half years...

Any ideas?
Mark

Mark
1990 Trooper LS 2.8 5-Speed
Stock and Slow