CH-46 D's were the mainstay of Navy Combat Support squadrons through about 2003. I think at the peak the Navy had about 120 CH-46D's in the inventory. T58GE-10 engines.
Navy and the few Marine Corp D's received SR&M upgrades in the 80's which included new flight control computers, new hyd plumbing, new wiring, and a host of other small upgrades (VHF/UHF radios). All in all it was still the same bird in many ways.
Remember the F was an offshoot - it retained the D's engines but incorporated redesigned cockpit, additional armor, and their was all weather/IFR formation capability that was later dropped.
F's became E's with the -16 engines.