Step 1 :Given the profit function P(x) = -x^3 + 4x^2 + x, we need to find the value of x when P(x) = 4 and x < 4.
Step 2 :Solve the equation: \( -x^3 + 4x^2 + x = 4 \)
Step 3 :The solutions are x = -1, 1, and 4.
Step 4 :Since we need a lesser number of T-shirts than 4 million, the company could produce \( \boxed{1} \) million T-shirts and still make the same profit of $4 million.