5.2L engine "bogs" ...here's the senerio, most noticable at 60+ mph, taching approx. 2000 rpm, lift off accelerator, and rpms drop to 1750 then engine bogs and rpms drop instantly to 1250 then rpms jump back to approx. 1700, and all is fine. This only appears to happen when rpms are decelerating and accelerator is lifted. Has anyone experienced this? Any help as to why? Thanks.