WordNet (r) 3.0 (2006):

painstakingly
    adv 1: in a fastidious and painstaking manner; "it is almost a
           waste of time painstakingly to learn the routines of
           selling" [syn: painstakingly, fastidiously]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "painstakingly":
   assiduously, carefully, cautiously, circumspectly, considerately,
   diligently, dingdong, earnestly, exhaustively, heedfully,
   industriously, intensely, lovingly, meticulously, mindfully,
   regardfully, sedulously, solicitously, tenderly, thoroughgoingly,
   thoroughly, thoughtfully, unremittingly, with care,
   with great care