Internet Speed Issue

Hello,

  For the last few months I have had issues with my connection speed.  I have replaced the splitter 4-Way 5-2500hz GE twice so far and also replaced the splitter running between the Cable modem and the TV upstairs twice.  That seemed to fix the problem for about a month and then it would start acting up again.  Now if I put a splitter in before the modem I get 6mbps.  If I connect directly to the wall I get 36.  I tested my connection coming from the Cox Box and I get 36 there as well.  I have noticed my power levels for my Motorola SB6121 DOCSIS 3.0 Modem are lower than what they should probably be according to what I've read.  I can't figure out if that's the wiring and 2 splitters in the house or the levels coming from the node.  I bought a 6 way 5-1000mhz Digital Splitter to change out the splitter on the outside of the house.  I will report my power levels off the modem this afternoon.  In the meantime any ideas?  Or Suggestions?