Here is the model to estimate the impact of free trade agreements (fta) and preferential trade agreements (pta) on exports (exports) for annual data from 1990-2018 with 4 year intervals:

ppmlhdfe exports fta pta , a(im#year ex#year im#ex) cluster(im#ex)

The value of pseudo R2 remains as high as 0.99+, and it stays there for various model specifications. Should I doubt something for this? Is there some alternative measure I may additionally calculate?