The Nissan Path

So this Friday I packed my surfboard and gear for a surfing road trip in my 1995 Pathfinder SE, I noticed it took quite a bit more power to move but I figured it was due to all the cargo in the back. That is until I started to go downhill, it was slowing down! I had to accelerate or else Id be going way too slow. When I tried putting it in neutral, it would keep its speed a little better but still slow down quite a bit. And when I say hills, I mean big BC hills at like 18%. I brought it to Canadian Tire and then a transmission shop and neither could figure out the problem. It seems if you let it sit for a long time, it gets a little better so maybe its the transmission or transfer case getting too hot but I don't know. Any help would be appreciated and if you need more info I'll be glad to share.

Thanks

check the fluid in your diffs and t-case. Sounds like maybe binding somewhere...

The fluid levels are all right, I just topped them off.

Any check engine light?

Nope