1999 E300 not shifting into 5th?

[TheKulakKing]

Hey everyone new member who finally got his dream car: a '99 E300!

This car has 250k miles on it so I fully expected it to have issues that needed addressing. First on the list of thing to fix is excessive fuel loss at motorway speeds. Driving 50 miles the fuel gauge indicated I burned through 1/4 of a tank. I could smell no diesel and could see no fuel leak anywhere. Thinking it might be a stuck injector I took a heat gun to the exhaust manifold ports of each cylinder as well as the exhaust side of the turbo charger, here are the temperatures in degrees F at operating temperature and being driven for a bit:
1)255
2)288
3)293
4)285
5)275
6) 270
EX turbo) 310

With a variance of temperatures right at 10% at the exhaust ports, that seems okay. Great! No fuel leak and no abnormally large variance of exhaust temps, now what? I noticed on the short drive back that at 70-80MPH engine speed was hovering at or in excess of 3K RPM. I've driven other 5 speed autotragics before and at that same speed with similar gear ratios and diff gears that I'd be at 2500RPM max. There were also some intermittent hard shifts but could no replicate on demand. There is also an intermittent CEL for the turbocharger wastegate solenoid. My thoughts on the problem are either:
A) Transmission is not shifting into 5th for some reason strictly with the transmission
OR
B) The wastegate CEL is related to not being able to shift into 5th and is also at least partially responsible for the intermittent hard shifts

Thoughts on this problem? Could it be something else I've missed or not thought of? Any help or insights would be greatly appreciated!