Switched to Synthetic, Change Filter Early?

[shertex]

On the 91 300D I just picked up, the PO kept on top of oil changes, but always dino (usually 15w40). Sometimes 5,000 mile intervals, other times as little as 1,000 (she didn't drive it very much in recent years).

I just switched to Mobil 1 Turbo Diesel Truck 5w40. Even though there are only 78,000 miles on the car, and even though PO did regular oil changes, is it likely that deposits/crud has built up that the synthetic oil will loosen....and thus should I replace the filter after, say, 1,000 miles?

I've just never been clear as to whether the build up the occurs with dino happens only on really high mileage vehicles where perhaps oil changes have been neglected or also on vehicles like mine.

Thanks!