Can one say " je trouve que c'est difficile à croire" vs "J'ai du mal à croire?" or is the latter the only way to say I find it difficult to believe.

One would probably choose one from among those different ways (but there are, of course, more):

Je le trouve difficile à croire. -- I find it difficult to believe.J'ai du mal à le croire. -- I have problems believing it.Je n'arrive pas à le croire. -- I can't (manage to) believe it.