I think the two are probably unrelated. Check if you get a vacuum in the fuel tank after driving for a bit, you may have a plugged tank vent. Could also be plugged fuel filters, plugged air filter, plugged exhaust.

Not shifting out of first is a classic symptom of the kick-down switch stuck in the down position.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC