If you're accustomed to the tone of a metal-covered Tele neck pickup, pretty much any uncovered (or plastic-covered) replacement is going to sound a good deal brighter -- and if the cover is brass (as the '52 RI's is iirc) instead of the less disruptive nickel silver, that difference is going to be even more pronounced. To my ear, the L-280TN is pretty much a sonic twin to the Strat-sized L-280SN -- iow, it performs like an exceptionally good noisefree Strat pickup, which I personally like much better than any traditional (single-coil w/metal cover) Tele neck pickup. I have a hunch you'd be happier with a (BL-designed!) Fender SCN -- it has a metal cover and the tone difference between it and a traditional Tele neck pickup isn't quite as big a leap.

Your low E string problem sounds like a setup issue that was masked by the muted high-end response of your previous pickup -- BL pickups are famous for revealing that sort of stuff.