All my variables are stationary, so cointigration can't be the problem. I have included one lag of the dependent variable and 5 explanatory variables. When I remove the explanatory variables, the R^2 doesnt change very much, only when I exclude the lag of the dependent variable, the R^2 is drastically reduced. I also checked the residuals and they dont seem to violate any assumptions.
Residual standard error: 0.005334 on 157 degrees of freedom Multiple R-squared: 0.968, Adjusted R-squared: 0.9664 F-statistic: 594 on 8 and 157 DF, p-value: < 2.2e-16
What could be the problem?