Have to chime in with a number of others here - seems there are a tad too many "5's" out there for tech advances - especially for 1943. Don't know if the developers have already though of it, but, one thing I've come up with would be to "cap" the number of highest level units for the first turns after a tech breakthough was made. Limit the upgrades to 1-2 units. This could be gradually increased, simulating a ramp in production.
Another idea that could work alongside this would be to adjust the size of the cap depending upon the level of the tech advance. For level 1 or 2, no big deal, a nominal cap & you can upgrade lots of units to those levels in fairly short order. For level 3, a more noticeable cap. At level 4 things would get pretty scarce. For level 5, units would be ultra-rare.
Another thought is a temporary drop in organization/readiness to go along with an upgrade, to simulate getting the new weapons out, the training of the crews & unforseen problems. Think Panthers before Kursk.
My apologies if somebody's come up with this stuff already... I'll be sure to drop my cheque for 2 cents in the mail later today...