What I've seen about the various "executive" F units is that they are mechanically and electrically GP38-x's. Single 645 engine, updated traction motors and electrics. The -x being variable depending on what type of electrical cabinet and control system was used. Maintain using standard parts, though with the freight fleet moving to 710 and newer engines (for power and emissions) the "standard parts" might be harder to source now.

UP's E units almost certainly have something similar, but probably they're not "GP38" because the E units need more power than that.

I think they're shedding the fancy units because nobody wants to run office car specials any more. What's the operating cost per hour and how does that compare to, say, a Gulfstream, for moving executives around the system? Nobody's going to entertain shippers (real or potential) on a train any more. Unless you're a UP that keeps a couple of steam engines (and some old diesels) around for the lulz. Plus, 645 engines are no longer "standard parts" on the big railroads; most of their freight power (if it's EMD) has moved on to 710 and newer engines.