can mine BTC but issues with LTC

[AmDD]

I have a computer thats having problems with litecoin mining on one GPU. The specs are as follows

GPU0: 5850 connected via riser
GPU1: 5850 connected via riser
GPU2: 5770 connected via riser
GPU3: 5850 plugged directly into motherboard
1050watt PSU
OS: BAMT setup to mine litecoins with CGMiner

I can mine bitcoins 24/7 for weeks on end with zero issues with this system, however when mining litecoin GPU3 dies within the first hour after starting to mine. Ive tried reducing intensity and the overclock to stock speeds, neither helped.

Any ideas?