1999 5.4 misfire
 

I have a 1999 Ford F150 with the 5.4 motor . the truck has 180,000 miles on it.About a week ago it started to misfire under a load.The check engine lihgt finally came on with a code of misfire on cylinder #1.I changed the coil pack on that cylinder with no change.Then i swapped the new coil pack with another just to be safe with still no change.the misfire is getting increasingly worse and now the check engine light flashes.

No where in your post did you mention changing the spark plug, did you change the spark plug? How many miles on the plugs, they wear out so might be time for a tune up.

The spark plugs have less than 20,000 miles on them,but i will still do that just in case.

yea, pull that plug and change.

I've seen problems with not using motorcraft plugs and fords tend to hate bosch plugs but your problem could also be due to a bad injector or lack of compression

Use the Motorcraft double platinum spark plugs, change every 90K - 100K miles. You will have less problems in the future.