I've had a lot of pinkie tension issues. I've managed to all but eradicate it in my left hand and significantly reduce it in my right hand.
Nw746's "chaining" if I'm correct on what they meant by it, is one of the methods I use to find relaxation at tempo for fast passages. I think of hand positions. If you keep your hand in the first position of an arpeggio, it's pretty easy to stay relaxed even at high speeds. So if I'm having tension issues, I first play one hand position at a time, pause, and go to the next for the phrase or series of arpeggios I'm working on. You should be able to stay relaxed with a stationary hand, so you know it's possible to do it.
The next thing I do is to connect hand positions, work on playing hand position 1 and hand position 2 together. Play it first at a moderate speed making sure you relax, and watch your hands as you increase speeds. Increasing speed you can sometimes be jerky, and this makes the transition between hand positions more tense. One of the things I noticed that I was doing is that my hand would start moving towards the next position before I finished playing the notes of one position. So what was happening is that my fingers would actually have to reach somewhat laterally to sound the arpeggio's notes, which caused a lot of tension and made my pinky fly up to compensate for that tension. So I focus on making sure I play all the notes in the hand position I am at in a relaxed manner, then shifting to the next position and doing the same. If there are a series of fast arpeggios covering a couple octaves and going up then down and vice versa, I isolate into groups of two hand positions every part of the arpeggio. Once I can do those isolated two-position arpeggios in a respectable tempo with relaxation, I start doing three, etc. until I can play it all with little tension.
Having a teacher would be really helpful for issues like this, because a lot of variables go into patterns like these. Rotation and arm movement can come into play (herky jerky elbow movement can make the fingers tense up to compensate) in ways that are difficult to describe in words.