Engine loses power after 5 minutes

[ncsdaonex]

I have a 94 ranger 4.0l, 5 speed 4x4, I bought the truck totaled and had a lot of trouble getting it running right, but its running pretty good now just seems weak after 5 min of driving, I tow with it and my other 4 cylinder ranger can pull my race car just as fast as it can so somethings wrong cause a v6 should have more power than a 4 cylinder, so any ideas? it seems more peppy the first 5 min of driving, also I can barely spin the tires on it if that helps at all.

 

[CheapThrills]

so once it starts to get hot you lose power? maybe low oil pressure?