Is a Sprinter for local delivery/Courier work overkill?

Generally, on "normal duty" I go about 6-7K miles, using regular Pennzoil. Not had a lot of good luck with longevity regularity stretching to 10K on gas engine. Not engine failure issues, but after about 150K tend to get more smoke out the tailpipe than I'd like. This is a 14 year old van, only 138K on the clock, I"ve put the last 12K on since March. I"ll probably be a bit on the cautious side until I get a bead on how well it's going to perform. So far so good. Did change out ALL the fluids after I bought it, engine, transmission, differential. Transmission fluid looked normal, no issues so that was good.