Actually, based on a quarter of a million dollars worth of friction coefficient research that my employer at that time funded for me to get done by a contractor, there isn't a significant difference in the preload generated by bolts torqued up dry and bolts lubed up with motor oil, the reason being that motor oil doesn't contain the type of anti-friction additives that significantly reduce the friction between the threads and the nut and between the nut and the clamped surface. It feels like less friction when you spin the nut up by hand to first contact, but once you start generating the loads that arise from applying the required torque value, the extra smoothness of oiled threads vice dry threads isn't a factor. Molybdenum disulfide is a totally different matter; anti-seize compounds that contain that require about a 50% reduction from a dry torque table value. The more common anti-seize compounds with graphite and some metallic additive (usually aluminum or copper, sometimes lead) in a petroleum carrier also require a significant reduction over a dry torque table value - on the order of 30-35%.
Nothing wrong with using the torque specified for the rod bolts by the engine manufacturer with engine oil as a thread lube. The tightening procedure you use can make a big difference, though, due to a factor called short term preload loss - this may be the reason that the nuts are coming loose. Tighten the bolts up to the final torque using either 3 or 4 equal steps (more, smaller steps don't gain anything). After applying each step, do not apply the next step until at least 2 minutes have elapsed - longer if you desire (the bulk of short term preload loss occurs in the first 2 to 5 minutes after each step is applied). When you have applied the final step, reaching the specified torque, leave it for 5 minutes or so, then come back and conduct a check pass, re-applying the final torque. If neither nut moves, your done. If either one moves during the check pass, leave it for another 5 minutes or so, then again apply a check pass with the final torque. The second time you apply the check pass, neither nut should move, but if either one moves, just keep re-applying the check pass until neither one moves.
And you don't want to know how much the device that measured the preload at a specific torque cost, lol....