The main result of the paper is the Aleksandrov–Bakelman–Pucci–Krylov–Tso (ABPKT) maximum principle for \(L^{n+1}\) -viscosity sub/super-solutions of fully nonlinear uniformly parabolic equations \(u_t+F(t,x,u,Du,D^2u)=f(t,x)\) in \((0,T]\times \Omega ,\) where \(\Omega \subset {\mathbb {R}}^n.\) In this version of the maximum principle, the \(L^{n+1}\) norm of f is taken over the so-called contact set. Equations have measurable and unbounded terms and we assume that the “drift” term which governs the dependence of F on the gradient variable is unbounded and is a function in \(L^{n+2}(Q).\) Other versions of the ABPKT maximum principle for \(L^p\) -viscosity solutions and its pointwise version are also obtained. We use the maximum principles to prove various properties of \(L^p\) -viscosity solutions and build basic theory of \(L^p\) -viscosity solutions for uniformly parabolic equations with the unbounded drift term.