The Full F-stat output from 3dDeconvolve is a measurement of the fit to the selected model (corresponding p values and computed q-values are shown in the AFNI GUI). Also the -fitts option to 3dDeconvolve gives the fit using the model at each voxel. By using the graph options "Tran 1D" Dataset #N plugin, you can see how well the plots overlap in the graph windows between the fit time series and the concatenated original time series.