Headlights go off and on while engine is on or off

If this is "fly by wire" throttle, any misalignment between gas pedal and TPS will cause this issue. Failure of the gas pedal sender is so common Lokar company makes a replacement pedal unit that is much better than stock.

I would say your heads have overheated and are likely warped. I would shop around for another engine.

small trucks like that are considered 1/4 ton. silverado 1500 1/2 ton an silverado 2500 3/4 and up. same goes for gmc

Well, it could mean that the emergency brake has not been fully released.The ABS system light is on if something has occurred within the ABS system. Something faulty may have happened there, get it checked out!

2wd or 4 wd and which motor you have so can futher help you

Is this a gas or diesel? Usually this is to protect an engine if there is a fault found by the truck's computer. It can be related to oil level, temp, or pressure. Could be related to the antifreeze. Check the levels. Also you said something about a headlight being dim. So You will need to check that Curcuit out as well. Could be related but a scan-tool would be needed to look a parameters.

shes easy , two bolts and two plug wires cant screw up , worst part is the room you have to work with , try get front of truck off the ground so you can manover

NO , just replace the the gasket and exhaust bolt, just make sure you buy a stainless bolt, there not much more but they will out last the truck. and might as well replace the drive's side too since your working on it. Good luck and hope this helps. 

You will usually find that it is the model number.
Or maximum total weight of vehicle.
Check your drivers manual

I had a dodge ram 2500, which only had a 1/2 ton capacity.
good luck

I had a problem with the brakes on my 2005 GMC that significantly increased the fuel consumption. The calipers for the disk brakes were not moving freely and were causing the brake pad on one side to always contact the rotor. This problem is easily found by checking for heated brakes after a short drive or by coasting to a stop to see if the truck rolls easily without power.