Hello guys.

My problem is, that when I alternate pick PM-ed 6th low string like this and then hit a SINGLE note on the 5th low string in high tempo, I hit them together and then it sounds like crap.
I have no problem with it until I reach tempo higher then 130 BPM.
Then I start "chunking" those 16ths and I can't hit the single note clearly.
Galloped rhytms are no problem, triplets too.
How should I build up my muscle memory in my picking hand effectively- metronome is obvious.

Thank for any help.
Home in on the problem which in this case is string crossing, and make an exercise out of it. That way you will be focusing on the problem as a separate entity, rather than the riff/lick as a whole.

Play it slow and accurate. It should feel effortless, relaxed, no tension.