@vondox No, you can switch between techs as you like, you don’t HAVE to stick to a tech each time.
The idea is that you spend 36-39 getting to Step 2 on as many different techs that you consider useful, and then you work on completing them.
You can easily get to STep 3 on one tech, but then want to spend your dice elsewhere. Think of it like assigning scientists to working on specific weapon specs and technologies - their notes don’t just get deleted if they get sidetracked and start investigating advanced artillery instead!
Germany and the US are indeed meant to be pretty tech heavy, yes. But that’s the point! The US will peel ahead and be able to lend lease units to Britain and USSR once they’re able to, which helps keep them strong.
The rolls themselves come from your major factories - every Major gives you 1 dice roll, plus Germany gets an extra one for free. USSR also gets one if they sign the Molotov-Ribbontrop pact.
A common move for Germany and USA is to immediately upgrade one factory on turn 1 to get access to an extra roll, as Germany is sitting on a medium factory in their home country.
Also, something I tripped up on, remember that captured Major factories act as a Minor factory, so after taking Paris’s Major, Germany does NOT get an extra tech roll.