I recently lost all spark on my 1990 f150 302. Which turns out it uses autolite 2545 plugs, so it has e6se heads from 86 mustang, crown vic etc... Anyway when I lost all spark. I had to replace the distributor for the pick up going bad. While doing that I replaced all gaskets from intake manifold and all the way up. Had coolant leak.. Just got it all wrapped up got the timing close by hand until I find a loan a tool place ro loan out a timing light. But my problem is when the truck is idling it does this perfectly but when I give it gas past a certain rpm it wants to decrease rpm to about 1500 and hang therw a few seconds before dropping back down to normal idle range..

Any ideas??

 

I had an issue where I'd slow down but the engine wanted to keep going, then, after a few seconds it would calm down. Sounds kinda like what you're experiencing. I cleaned out the idle air control valve with some Gumout Carb + Choke cleaner and the problem went away.