I've spent many hours "picking over" my own instruments, but...

[bloke]

[bloke]

To drastically improve tuning characteristics requires "punting", such as they did in Markneukirchen (a couple of decades ago) when they pulled the out-of-tune 2155R (rotary) off the shelf, dusted it off, completely retapered it's BUGLE, and released it as the (very manageable intonation) model 5450.

Changing mouthpipe tapers, cleaning up the interiors of messy solder joints, deepening or diminishing receiver depths, locating and eliminating very subtle air leaks, or even moving a main slide from before-to-after a valveset does little-if-anything to alter intonation characteristics.

[Three Valves]

Of course not.

What you need is a new mouthpiece!!

[Casca Grossa]

Maybe switch to an American made, student model trumpet or trombone. It will probably play more in tune with almost no tweaking compared to a $xx,xxx professional, silver plated, 5 or 6 valve tuba.