The last Test series that the West Indies played was against Australia....
1) Nash was the fourth best run-getter on both sides. His 250 runs came at a good average of 41, and was only beaten by Gayle (346), Katich (302) and Watson (263). To drop him after such a good performance with the bat would be ridiculous!
2) Test cricket is played over five days. This is not 20/20 cricket. It doesn't matter if Nash scores slowly. Shiv can also score slowly. Dravid scores slowly in Test cricket. Larry Gomes used to score slowly. All are/were great Test batsmen....
3) None of the Tests were drawn as a result of slow batting. So, both Shiv and Nash can play in this WI side, if they deserve their places.