I don't think anyone can tell 'what it is' exactly. Make sure the new lamp is plugged in firmly and the wiring is good....no charred wires to the lamp. They get pretty hot. I'd put the old lamp back in to trouble shoot....did you buy the new lamp WITH housing? Save the old housing if you did.
Are there any flashing lights when it fails?....look on the front of the TV than check the manual. That's where to start.
An instant shutdown? No burning smell? Maybe clogged cooling fans?
Can you unplug....than open for a look? Make sure the color wheel freely spins? Get the dust out of fans? Look for anything obvious?
1. The new bulb may not be compatible; reinstall the old assembly.
2. Note that there is a small switch near the lamp door cover. The switch is an interlock that prevents turning on the lamp with the cover removed. Even with the cover in place, it is common for the switch to open after a short time of operation due to a very slight expansion of the cabinet as it heats up. The solution is to permanently close the switch. A twist tie, or tie-wrap works nicely.
I have the exact same TV and mine would sporadically turn off. Sometimes after a few mins.. sometimes after a couple of hours. What I did was take the rear panel sensor switch (little blue switch like thing on mine) and make sure the connector leads were clean by carefully plugging and unplugging the connector. This will score the metal leads and break up light corrosion that can accumulate. I also put a piece of electrical tape behind the the board where it screws to the plastic mount to sort of force it to make more contact with the striker on the read panel as the panel is reattached to the back of the TV. Since doing this my TV has not turn off once on me.