How much oil are you talking? Isuzu states that 1 qt/1000 miles is the norm, but I don't believe every Isuzu uses that much.
Mine doesn't.
The hard starting - has this just started, perhaps following a real cold weather snap? If so, try a bottle of HEET (gas water remover) in your tank.
My '97 was doing this just a few weeks back, discovered it was the cheaper gas station causing the problem. I was also experiencing hesitation, rough idling, and it stalled twice.
Went back to my normal Shell gas station and within 14 miles, all symptoms subsided.
Otherwise, check all electrical connections, and the output of the battery and alternator. If your battery is more then 3yrs old, I'd look there first.
Colorado got hit with an Artic weather snap - 2 trucks were zapped with effects. 1 truck, the '85 Toyota, busting 2 radiator and a heater core hose, the other, the Rodeo, busting out the radiator hose that connects to the oil cooler.
Nothing like literally having a RIVER of antifreeze rolling down the driveway from two vehicles - on the same night, no less

There's nothing worse then standing outside at -15F, attempting make-shaft hoses to fit areas where, of course, calls for pre-molded hoses.
I will firmly now go back to changing out radiator hoses every 2 yrs, I will not push for just whenever they "look" or feel bad. These particular vehicle's hoses all "looked" great.