The torque/hp cross-over point for a 1954 235 truck engine is about 2,500 RPM. My Suburban has the 3.55 conversion and 215/85x16 radial truck tires that have a loaded diameter of abut 31.5 inches. I can comfortably cruise 300 miles at either 60-65 MPH (2450 RPM) and get about 18 MPG, or at 65-70 MPH (2650 RPM) and get about 12 MPG. I bought a speedometer adapter for about $100 - it's nice to know how fast your are going (as a policeman told me before I got the adapter).
I realize that the improvement provided by the 3.55 was not very much but it allows me to keep it looking original (different strokes for different folks).
The improvement in interior noise was noticeable to me and my passengers, even though my interior noise was quite low before the 3.55 conversion. I strongly recommend using the gear/bushing/etc installation kit if the 3.55 conversion is being done.
