Thread: i have a cylinder #1 and #5 intermediate misfire

If you have the original wires on it change them. Old wires can "crossfire" and if it's a '99 it's time anyway. #1 and #5 run in the same plastic loom across the front of the valve cover. You can get OEM wires from ZZP for $35 or it's a dandy time to upgrade.

Next, change your coils. They run about $25 each. I would be surprised if it was an injector problem.
Sounds like a problem I had with my F350 SuperDuty. Ran fine from 0-37 miles per hour. Anything over that and the truck bogged and kicked. It would NOT set a code. Turned out to be the #6 coil (It was a V10). Changed the coil and problem solved.