they where exchanged at borders wasnt that due to fuel issues and it was decided to send the T34 to defend the mother land it wasnt a straight swap
What defense of the motherland? In January 45 the Red Army did not defend the motherland anymore... They were knocking on the German door...
it was eiser to train normal guys to use a T34 than a sherman, it was more to do with logistics than any thing else.
It had nothing to do with ease of training. They issued the Sherman tanks to their best units because they were simply better:
-they were more reliable, which made them more useful in breakthrough exploitation (something the Guards units were expected to do)
-they had optical sights far superior to those on T-34s
-they had superior guns (US 75mm gun was FAR superior to the 76.2mm gun on T-34, also in terms of armor penetration, US 76mm gun was simply better than 85mm on T-34)* - so the US 76mm gun line goes above the 85mm one ;-)
-the three man turret allowed the tank commander to actually command the tank instead of acting as a gunner
-they had pretty much the same protection. You were hit by a German gun, your tank was destroyed. Period.
-oh, and did I mention radios. In every tank. WORKING ONES. RELIABLE. They allowed the Guard units to use something resembling tactics, not just an "Urrah!" charge across the field - a real coordination of their actions.
One additional thing you seem not to understand. Comfort is very important to tank crew (or any vehicle crew). Why? Because after a hour-long trip inside T-34 you are in no shape to fight. You'll be barely able to walk, won't be able to think clearly and will loose combat with enemy equipped with inferior, but comfortable tank. Those are the facts of life. Comfort is not a luxury - it is a necessity, as the most important component of any vehicle is its crew.
You don't give your best weapons to half-trained conscripts. You give them to folks who will be able to use them. The half-trained conscripts get the mass-produced crap. The fact that Soviets equipped their Guards units with Shermans whenever available says something about what they really thought about those tanks.
* - Take a look at this. The diagram shows penetration of various Soviet-used guns at various ranges. X axis is distance in meters, Y is the average penetration. The dashed horizontal lines represent protection of various German tanks. The yellow line is the performance of T-34's 76mm gun. The red line is the Sherman's 75mm gun. The pink line is the 85mm gun. The US 76mm gun is not on the diagram, but - to quote a sentence from the Soviet report on King Tiger:
"American 76 mm armor-piercing projectiles penetrated the "Tiger-B" tank's side plates at ranges 1.5 to 2 times greater the domestic 85 mm armor-piercing projectiles."