hi, I wonder if you know about Form by Jos Vermaseren (took lots of ideas from Schoonschip by M. Veltman. As you do physics my guess if that you might know about it. If not have a look at it, some of the ideas might be useful (freezing expressions left over after taking out some factors to work on them independently -- special "combining" substitutions that add an arg to a function
Id, x^any * f(x1,...)= f (poly(x), x1,...), poly(x) = full polynomial in x of all terms having f's
useful for integ.