We develop a modified power-counting within the heavy quark effective theory (HQET),
that results in a highly constrained set of second-order power corrections in the heavy quark expansion, compared to the standard approach. We implement this modified expansion to determine all ˉB→D(∗)form factors, both within and beyond the Standard Model, to O(αs,αs/mc,b,1/m2c,b). Using measured ˉB→D(∗)ℓˉν differential branching fractions for light leptons (ℓ=e,μ), we constrain not only leading and subleading Isgur-Wise functions, but also the 1/m2c,b corrections from subsubleading terms. We provide updated precision predictions for ˉB→D(∗)τˉν decay rates, lepton universality ratios, and the CKM matrix element |Vcb|.