If there is a vibration or noise at highway speed, it could be from the frontdrive shaft and may require replacement of the double cardan joint. A double cardan joint is a type of driveshaft joint that uses two universal joints.
Problems for specific Ford F-150 years:
Car problem reports
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Newest reported 1999 Ford F-150 problems
There is a technical service bulletin for the V8 engines regarding a possible problem with the spark plug being ejected from the cylinder head, damaging the threads in the spark plug hole. If the vehicle is under warranty, cylinder head replacement is recommended. If the vehicle is out of warranty, Ford authorized the use of a specific thread insert to repair the head.
Turned on heater and got cold air. set it to 90 and the the temp guage got to half and only got a small amount of heat. vehicle started to have windows fog had to turn on A/C to clear them. It was working fine just two days ago last time used.
If a noise from the rear end is heard when going around turns or after driving at highway speed for an extended period, there is an updated differential clutch kit available.