My truck has similar issues with 276K on the clock. Got in in Feb with 258K, have done numerous wheeling trips out to the Black Hills, Drummond Island, etc.
Started out using Mobil 1 synthetic for OCs every 3K for the first 3 OCs or so, and the engine would go through MULTIPLE quarts between changes. I brought at 5 qt jug out with me to the Black Hills the first time we went back in May. Then switched to full conventional 10W-30 to see if this would reduce my oil loss. It's help dramatically, with losing a quart or less between 3-4K OC intervals. I have horrible valve seal leaks that need to be addressed- the undercarriage looks like a horror movie.
Also slow coolant loss, and I also notice a good amount of white smoke in the mornings when I crank her over. Haven't been able to decide if it smells sweet, though. I've always turned my key to ACC to let the fuel pump work before cranking it over in all of my vehicles, and my idle with this truck is pretty dang solid. My rear heater line burst a few months back on the trails and did the quick rear heater bypass method, and filled the system back up with coolant and properly burped the system. Still slow coolant loss after this. My radiator is also original, so that would be worth replacing, too.
At this point for me, even with the leaks and losses, the thing still runs solid. When/if the engine does go, I'll be looking to ideally replace it with the 4.7L iForce. This old girl has worked hard for me since I've had it, and this poor old 3.4 doesn't owe anybody anything. I know I could rebuild it, but it might be better to just let old dogs lie. Although, to have another 3.4 out there running past 400K sounds cool, too...