Is it only when the truck is running? It might be a good idea to measure voltage at the battery with the truck idling and revved up to like 2k rpm to see what it does.

Is it possible you have a wiring issue going to the headlight bulbs? How were the Hella's wired in? Do they have their own power source and a relay or were they piggybacked off the stock lights wiring?

 

If you had this set up for at least 2 years and it's now acting up I'd say your alternator is on it's way out. But go cheap and easier first, check the battery.

 

yea they have their own independent switch, relay, everything

 

Simple way to find out if your hella's are on their own circuit(relay) and not piggybacked.

Turn your hella's on, if they dim like your head lights, then its battery/alternator.
If they don't dim, then its a wiring issue withing the head lights circuit. Could be a relay, fuse coming loose, turn on lead coming loose, etc. Let me know when you do that, and maybe I can add a few diagrams to help you better diagnose the culprit.

Do they do this on both, high and low beams?

 

That's a good idea. And yea, they have their own relay and wiring. No piggyback at all.

Last night driving home while the hellas were on I again had the headlights dim, come back...dim...come back. The hellas stayed the same. So I'll check everything on the headlights

 

I would start check the wires on the headlight plugs themselves then backtrack to, relays, and fuses. Anything could be loose

 

sounded like a bad alternator or battery, but if the hellas are fine, yup, decent chance something in the lights are acting up. hope it's nothing serious