\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) - \left ( 1/30\,{\frac {{\rm d}^{4}}{{\rm d}{x}^{4}}}p \left ( x \right ) +7/3\,{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}p \left ( x \right ) +ap \left ( x \right ) +b \right ) y \left ( x \right ) =0} \]
Mathematica: cpu = 0.258033 (sec), leaf count = 37 \[ \text {DSolve}\left [y''(x)-y(x) \left (a p(x)+b+\frac {p^4(x)}{30}+\frac {7 p''(x)}{3}\right )=0,y(x),x\right ] \]
Maple: cpu = 0.172 (sec), leaf count = 48 \[ \left \{ y \left ( x \right ) ={\it DESol} \left ( \left \{ {\frac { {\rm d}^{2}}{{\rm d}{x}^{2}}}{\it \_Y} \left ( x \right ) + \left ( -{ \frac {{\frac {{\rm d}^{4}}{{\rm d}{x}^{4}}}p \left ( x \right ) }{30}}- {\frac {7\,{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}p \left ( x \right ) }{3 }}-ap \left ( x \right ) -b \right ) {\it \_Y} \left ( x \right ) \right \} , \left \{ {\it \_Y} \left ( x \right ) \right \} \right ) \right \} \]