If a locomotive (locomotive A) pulls another (locomotive B), when locomotive A runs faster than locomotive B, locomotive B will slowly be away from locomotive A and finally lost its connection.
And the "strange problems during turns" if it isn't the back of the locomotive linking together.

Also I suggest a "Extreme Long Straight", maybe 1x12 or 1x9?
And I'm looking forward to the new tracks in #48.

Pulling slower trains isn't supported in TC.

The other request would go into that 48 thread. But our new system will work different so we don't need to add specific lengths.

Honestly pulling trains in general isn't supported, never was, it's even noted in the book. if you saw the logic behind the system, you'd get why, lol.
Aside from rewriting the entire linking and collision systems there's really no fix, so we've been just putting it off till the rewrite, where it does work.