Didn't have time to watch all the videos, and you didn't post any smurfy builds, but I looked at the MAD-3R builds.
Always bring Endo over FF, its just better. FF is to be used only after you have endo and still need tonnage and have a lot of slots.
In general the Marauder, especially the 3R with its focus on ballistics, doesn't run an XL well if you make full use of its ability to run triple AC5s. I did throw together a build real quick for it.
http://mwo.smurfy-ne...5e2dfc2deb13809
3 AC5, 2 ML.
One side of the mech is entirely empty, this is called a deadside. It acts as a shield for your mech with nothing in it to lose, the Marauder's shape is wide on the side profile and blocks enemies from hitting the other side and most of the CT if you twist fully, this will keep your important parts safe. Destroyed components when hit only transfer i think it was 50% of the damage to the component next to it, so if you lose your torso and then shield with it your CT can still take double the damage it normally would with proper shielding.
The triple AC5s are brutal when fired in solid bursts rather than staggered, they are more accurate this way and spread damage less, essentially hitting your opponent with the equivalent of a gauss round every second and a half. Firing all at once can be coupled very well with the deadside shielding technique, allowing you to fire, shield, fire, and shield in rapid succession, making you a very tanky and very dangerous opponent.
I also upped the engine to a STD300 compared to your build, this gives your mech some hope of keeping up with mechs faster than Dire Wolves and increases your torso twist speed to allow you to shield with your empty side.
I do believe ammo is less than your build, but if you fire all at once rather than stagger you don't need as much due to more accuracy and less spread.