Aha, at last! Your problem could be your upstream power level. Your upstream power level is 34, that is the signal level that your modem is sending, which is low. If you were in a crowded room talking to someone in a whisper, they wouldn't be able to here you very well. They might ask you to repeat yourself a lot so they could understand you. If you think of the cable t.v. plant as that crowded room, your modem is just whispering. This might cause packet loss, repeated packet sending, which you would see as a slow connection. You are probably at or near the end of a line with a low value tap (i.e 11,8,or 4), or the cable company has the return all screwed up. (I've seen techs turn up the return on an amp to fix a customer coming right off the amp with a high value tap, and effectively screw up everybody else on down the line). Since your downstream level is +5 (your modem tolerances are +15 to -15) you can attenuate 15 or 20 db. That is the equivalent of two 4-way splitters. Try feeding your modem with a four way splitter, if you have one, and see if it helps. That will raise your transmit level from 34 to 42. Another four way will raise it to 49.
This is CABL.com posting #188211. Tiny Link: cabl.co/mW7P