Dies on heavy load and takes several minutes to restart

[Johndeere4630]

I have a 07 6.0 with stock straight pipe, egr delete and had injectors replaced/repaired and new o rings for hpo rail.. My problem is when I'm pulling my trailer (30 ft gooseneck) hauling a tractor or round bales it starts to die out like I let my foot off the pedal n back into several times and then it will die. Once it dies I have to crank on it a long time and it will eventually start. My degas bottle pressurized quite a bit but no puking. It does fine just driving it tho, no puking or pressurizing unless I really get into it! I'm guessing from what I read n hear it my head gaskets but I hope not! thanks for any help.