I wish you luck. I'd get the engineer to check the upstream at the same time. It should be under 58, way under if possible. If close you might still have trouble (weather dependent I find).
It took me a year (and many days off work at my expense) to get mine sorted out with frequent periods of modem reboots. It was all down to signal levels. First the downstream and then the upstream (engineer ignored the upstream on first call out).
Upstream is far more difficult to get fixed as it's the power of the modem signal to the network that's at issue and involves sorting out any rubbish on the cable. You may need a new cable pulled especially if it's currently shared with one or more STBs (or if some muppet installed the cable split off your neighbour!

).
It's a lot of hassle I can tell you. The worst thing seemed to be the lack of real understanding by the techs you call, and no knowledge of your previous calls, so each time you've got to try and explain and they go through the same old routine of asking you dummies questions about your PC (i.e. "no it's not my PC, it's definitely the signal quality on the cable, you've had 3 people out before checking it, blah, blah, etc").
It took some rather more helpful tech on forums like this (well the old 'other' site) to sort it.
I've always maintained that BT's approach of testing the line and just refusing the application if the line is poor quality is better. Harsh, but better in the long run. NTL seem to think that as long as there's a cable there, anything will work.
Oh, and it can all go T.U. again if a neighbour gets a new install or there a fault in the green box (or some brat kicks the box in). It's at your expense to get it fixed by calling NTL and waiting in for an engineer only to find it's the box down the road, and I doubt your neighbours will praise you for fixing their cable.