Does anybody know which one has the better rail and tunnel extension kits? SLP is a little cheaper in price but I wonder who actually has the better quality product?

Track USA for sure, there rail extensions are custom made to fit right up to your stock rails and you are then able to use full hyfax on the extended rails. The slp kits look cheap when installed and u can't use full lenght hyfax. So if u are extending 121 to 136 u still use 121 hyfax.

I bought a set of the SLP on recomendation of my dealer. After i got them on I did not like the looks of them and thought they would be weak. Sold them and went with tracks USA. I have had the 136 extensions from tracks usa on 2 of my sleds. roughly 3000 miles and no problems. I like the full length look and hyfax. The tracks system requires some fine adjustments to match up, but nothing to get too excited about.

Do tracks USA, they are nice people to deal with.

mike