remove the injector lines. 15mm and 19mm. Make sure you mark where they go. pull off the rocker cover, scrape all the old gasket(if it has it) and rtv off, clean it, put a bead of black rtv on it and put it back on.
To bleed the injector lines keep the B-nut at the injector loose and turn the motor over 15 sec at at time, wait 1min between, untill fuel if squirting out the line B-nut. Tighten.
It is going to be tricky if you leave the intake manifold on there. You will probably have to take it off. One thing I wish i did before i started all this maintenance is take the truck to a self car wash and spray down the engine. especially the valley, and around the manifold.
Go to the Wiki on this site (bottom of main forum page) and there are links to maintenance manuals. What you are looking for will be in the intermediate maintenance manual
Good luck. Its a lot of trouble for a rocker cover leak. Not hard, just time consuming.