To the contrary Brian.
What breimer described is not even close to normal. A properly operating Case GT will travel smoothly in both forward and reverse and achieve the same ground speed. The speed changes are linear in either direction. The last of the tractors with the CASE logo displayed went down the assembly line in 1986. As such, all of the Case tractors are at least 27 years old and your 155 is at least 45 years old.
breimer's 442 is at least 41 years old. A lot of wear and tear can take place over those years, especially when they are owned by people who do not service them when they should.