Is your problem spotting tanks, or spotting tanks and then killing them?
It takes time for your eyes to adjust to see movement, or tanks that are hidden. Map knowledge also becomes critical, as you want to understand where most players tend to go. Here is a good resource by another user: http://warthunder-heatmaps.crabdance.com/
I played for about 2 months before I felt comfortable, where I can spot tanks or movement. That vision comes with time from playing. Did you have issues before you reached 6.7 or just now? Maybe move back to a 5.7 lineup and play there while you get more experience at seeing the battlefield.
The other big factor, is monitoring the battle around for your situational awareness. Good headphones, help as you can generally hear enemies before you see them. The other is note the names of teammates near you and monitor the kill feed and map. See one of your teammates die, note where and what type of vehicle destroyed them. This can be helpful as it tells you the enemy is near or watching a spot on the battlefield, but it also tells you if it’s a IS-3, that it has a long reload and may allow you to move or get a shot.
About your current lineup, they are not my favorites. The IS-2 have good guns, but a slow reload. Makes it tough if you miss your shot, as now you have to hide and wait for a follow up shot. The T44 is ok, although I prefer the T44-100.
The other issue, which is common to most Soviet/Russian tanks are the lack of gun depression which is always a problem at least for me. Makes me have to watch the terrain and judge where I can best make a shot. On hilly maps, pushing to the top in order to get your guns to bear, highlights you now and makes you a big target.
Lastly, getting critical hits (or any hits), taking caps, repairing teammates, can gain you just as many points as just killing tanks.