So they are the nt555 not the nt555r's?
Some Durango and Dakota factory rims are 18's but not to sure on width.
I was at that point too. Had a nice set of 17" rims/tires but needed more traction on the street. Ended up buying the XD Addicts 17x9 front which i could run my 275/55/17 Toyos tires and then brought 18x9 XD Addicts rears for my 305/45/18 Nitto NT555r DR's. the overall diameter is very close.