  Let $G=\text{GL}_n(q)$ be the general linear group over the finite field
$\mathbb{F}_q$ of $q$ elements, and let $k$ be an algebraically closed field of
characteristic $r >0$ such that $r$ does not divide $q(q-1)$. In 1999, Cline,
Parshall, and Scott showed that under these assumptions, cohomology
calculations for $G$ may be translated to Ext$^i$ calculations over a $q$-Schur
algebra. The aim of this paper is to extend the results of Cline, Parshall, and
Scott and show that Ext$^i$ calculations for $\text{GL}_n(q)$ may also be
translated to Ext$^i$ calculations over an appropriate $q$-Schur algebra (both
for $i=1$ and $i>1$). To that end, we establish formulas relating certain Ext
groups for $\text{GL}_n(q)$ to Ext groups for the $q$-Schur algebra
$S_q(n,n)_k$. As a consequence, we show that there are no non-split
self-extensions of irreducible $kG$-modules belonging to the unipotent
principal Harish-Chandra series. As an application in higher degree, we
describe a method which yields vanishing results for higher Ext groups between
irreducible $kG$-modules and demonstrate this method in a series of examples.
