I am curious: What is your division setup?
Remember that each province can only provide a certain frontage for your troops: 10 base + 5 for each other province you attack from. So even if you bring 5 panzer divisions to the front, they will not be able to fight simultaneously unless you attack from multiple directions.
And remember, tanks have a frontage of 2 per brigade before you research spearhead - that means a single ARM-ARM-MOT division will have a basic frontage of 5 without spearhead and 3 with spearhead - quite a difference!
Same goes for your infantry: Infantry has a frontage of 1, while all support brigades (ART, SP-ART, ENG, etc.) have a frontage of 0. That means a setup like INF-INF-INF has a frontage of 3, while INF-INF-ART-ART has a frontage of 2. So use support brigades in your division once you can cover the whole frontline. As germany I recommend INF-INF-ART-ART division to allow schwerpunkt offensives.