The 5100 is designed for lifted vehicles where the amount of travel has changed (typically increased). As such, Rancho has no idea how much lift a particular vehicle may have, so can't identify a specific shock for each possible configuration. For vehicles that have other then stock travel, the fully compressed and extended suspension positions, or OEM shock collapsed and extended lengths, must be measured and compared to the collapsed and extended length specifications of the available shocks (with the appropriate mounting configuration).
If the only modification is the 1.5" TT, then the amount of travel has not changed and the shock collapsed and extended lengths are the same as for stock. Find those and compare to the available 5100 shocks.
