As the StuG was designed to fill an infantry close support combat role, early models were fitted with a howitzer-pattern, low-velocity 7.5 cm StuK 37 L/24 gun, similar to those used by the earliest versions of the fully turreted Panzer IV. Low-velocity shells are lightly built of thin steel and carry a large charge of explosive, to destroy soft-skin targets and blast fortifications. Such shells do not penetrate armour well. After the Germans encountered the [Soviet]
(Soviet Union - Wikipedia) KV-1 and T-34 tanks, the StuG was equipped with a high-velocity 7.5 cm StuK 40 L/43 main gun (spring 1942) and in the autumn of 1942 with the slightly longer 7.5 cm StuK 40 L/48 gun.[4] These high-velocity guns were the same as those mounted on the Panzer IV for anti-tank use but the heavy steel wall high-velocity shells contained much less explosives and had a lower blast effect for use against infantry or field fortifications. These versions were known as the 7.5 cm Sturmgeschütz 40 Ausf.F , Ausf. F/8 and Ausf. G (Sd.Kfz.142/1) .
Removed stupidity
In 1942, a variant of the StuG Ausf. F was designed with a 10.5 cm (4.1 in) true howitzer instead of the 7.5 cm StuK 40 L/43 cannon. These new vehicles, designated StuH 42 (Sturmhaubitze 42, Sd.Kfz 142/2), were designed to provide infantry support with the increased number of StuG III Ausf. F/8 and Ausf. Gs being used in the anti-tank role. The StuH 42 mounted a variant of the 10.5 cm leFH 18 howitzer, modified to be electrically fired and fitted with a muzzle brake. Production models were built on StuG III Ausf. G chassis. The muzzle brake was often omitted due to the scarcity of resources later in the war. Alkett produced 1,299 StuH 42 from March 1943 to 1945, the initial 12 vehicles were built on repaired StuG III Ausf. F and F/8 from the autumn of 1942 to January 1943. ![StuH 42 | World War II Wiki | Fandom] 
In 1943, 10 StuG IIIs were converted to the StuG III (Flamm) configuration by replacing the main gun with a Schwade flamethrower. These chassis were all refurbished at the depot level and were a variety of pre-Ausf. F models. There are no reports to indicate that any of these were used in combat and all were returned to Ausf. G standard at depot level by 1944. 
I personally think the StuG with the StuK 75mm should be BR1,its much worse then comparable tanks like the Ho-I or Scott;as they are faster,have turrets with 360° traverse,and at least 1MG,and also have HEAT shells,which this likely won’t have since the StuG 3A has HEAT and is almost the same.The many cons (the main ones being low ammo compared to other short 75mms,no HEAT,slow,armour penetrateable by any BR1 tank with a cannon,and casemate) of this can let this be BR1 without being too broken, the other ones look good though.
Thanks i avoid ranking br1 as i am bad at it, what do you think of the stuh 42 and flampanzer
the StuH could work at BR3 IF it gets a few HEAT rounds to make up for it’s major shortcomings compared to the Sherman 105,but it could possibly be 2 if it only gets HE due to its other shortcomings (normal StuGs included).as for the Flammpanzer StuG,it would have to be BR1 if it were to be any sort of use,while the flamethrower jet could be much longer then the Flammpanzer II,it trades speed,a turret,MG,and all that for a bit more survivability and a bit better flamethrower.