Cowboy, I measured mine today, 1998 1500 Quad cab, two door, it was 134"
I think the difference are in the rear door option. if you look at the first truck the rear doors don't open. And on the second truck its rear doors open. And then you have the true four doors.
These wheel bases are from my Dodge book, unfortunately they don't tell you which ones are short beds.
1994 - 2001 wheel bases
118.7 in. (1500)
134.7 in. (1500)
138.7 in. (1500)
154.7 in. (1500)
134.7 in. (2500)
138.7 in. (2500)
154.7 in. (2500)
134.7 in. (3500)
154.7 in. (3500)
2002 - 2008 wheel bases
120.5 in. (1500)
140.5 in. (1500/2500/3500)
160.5 in. (1500/2500/3500)
160.3 in. (3500/1500/2500)