Top speed: You may have weak ignition, poor fuel delivery or other CVT problems. Start by removing the CVT cover and run the engine on while the vehicle is on stands. You want to look at the belt position in the pulleys and make sure it is traveling properly. Next step is to check your spark - Remove the plug and ground the threads against the engine.You should have a healthy spark otherwise look for loose connections to the coil or CDI. If this is fine, look for a lean or rich condition on the plug. Too lean typically means you have air leak in your intake or clogged fuel filter and too rich is either a clogged air filter or malfunctioning choke.
Reverse: There is fine balance between shifting to reverse and forward. What you described sound like the reverse cable is too tight and does not allow forward to properly engage. Loosen the cable tension half a turn at a time to see if shifting gets better. If your adjust is at the point where the cable is slack or reverse no longer engages, you will need to disassemble your reverse assembly and look for debris or damage.
2006 Tank Urban Touring 150SE
6" intake plenum, 1.5" UNI filter, K&N precharger, 130 main jet, NGK Iridium IX CR7HIX spark plug, MRP yellow adjustable CDI, Orange high output coil, 14Ah sealed battery, 2000 RPM red torque spring, Koso 115mm variator, Dr Pulley 12g sliders