Okay, you've done just about everything you could for that old typewriter to try to free up a carriage that goes just fine--provided you're typing speed is about ten words every five days.  A snail could have won the race faster.  You've cleaned and lubed the tracks and spring drum, seen if the body shell is pinching anywhere, and you've seen that everything is out of the way in the tabulator and the rest of the interior mechanism.  Ah, but there's one thing else that might be causing the slowdown--especially when you're typing:  The Escapement Wheel.  Those things, like the rest of the machine, can be gunked-up or rusted in.  Sometimes you can find old coagulated grease in the mechanism.  Cleaning a just a little oil where necessary will free things up there, but be careful--especially with the little springs here and there.  The mechanism there on the whole is a little like an old-fashioned ticky-tock clock.  I remember a typewriter friend of mine had a machine he gave me after trying to find what it was about it that was making the carriage slow.  I took it and waited until I could find a spare parts typewriter, thinking I might need to change out a part (I thought it might have been the spring drum).  I got the parts machine, and about the time I got it home, I thought to try cleaning and lubing the escapement wheel.  Sure enough, that's what it was!  I didn't need to change out anything.  I checked over the rest of the machine, and it was fine, so I then sold it to a lady who used it to type church bulletins (I used to have quite a clientele of church secretaries, as I outfitted a number of them with typewriters back in the l990s).