T4 - "Pattons Jumbo Shermans" - Shermans gain 25% health and 25% reduced penetration (Historically correct!)
Wouldn't this kinda make your tanks worse?
Or do you mean, Your shemans get penetrated less? If so, I guess that could work in a way, since its a T4...
T3 - Sandbag Shermans - Shermans can buy a 50 munitions upgrade that reduces penetration from handheld at by 25% (historycally incorrect!)
Sounds like a nice idea, but probally make the penetration debuff a little less. -25% seems a bit extreme, but I really don't know CoH stat's so I'm not in a good position to say.
T2 - Tank destroyers - M10's get a 25% reduced accuracy modifer
I guess you mean recieving? I guess that could work, although once again, 25% seems a bit much, but It wouldn't know
On board repairs give as many repairs as you want with 1.5 x higher cooldown
That wouldn't be fair in any sense unless the cooldown was EXTREMELY long, otherwise everyone would get this as a doctrine choice since of its OPness, and with a bit of micro be able to keep a pershing for example on from start to end simply because they can repair it, Which in no way would be fair....
Pershing is unlocked as a unit choice by picking any tier 3
If this was to be added, then Everyone else should be able to get their "tanks" like so, (eg, Terror getting KT with Tier 3 choice). I think it should stay as a upgrade like everyone else has to
Flank speed is not available on Mine Flail Shermans
Makes sense, This sounds like a good idea
Flank speed is now available on m10's at a reduced rate
Can M10's get Flank speed? If so, then It might be justiable, since they do rely on speed and turret speed rather then brute strength to take out tanks. If not, They should probally grant it as so.
Tungsten tipping now affects Pershings
I think the pershing doesn't really need the extra penetration, I believe they pentrate good enough for them not to need it, but I haven't really been up against too many Pershings, but they seemed able to penetrate easily enough.
That's my view of your Ideas, some Good, some Ok and could do with a little editing and some just bad
Edit-
I really have no idea what to say to this.
As you can tell, I did