I have amd dual graphics one is of 768mb and one is of 2048 mb but gta 4 is only showing 1468mb?

I bought my laptop 2months before and gta 4 was working extremely fine at ultra graphics. It was showing around 2800mb graphics and it should show that only but today when i was playing it i noticed it shows only around 1400 mb graphics and the performance in games like watch dogs gta 4 nfs rivals and saints row 4 has also decreased a lot. I also overclock my graphics card a lot. So does overclocking decreased the health of my graphics card. Now what should i do? Should i call in the sevice center and tell them to come and fix my laptop?

i have lenovo g505s 20255
it has
8GB ram
768MB ATI AMD Radeon HD 8550G (Lenovo)
2048MB ATI AMD Radeon HD 8500M Series (Lenovo)
amd a8 quad core with turbo boost technology of upto 3.1ghz
931GB Seagate ST1000LM024 HN-M101MBB (SATA)

Over clocking should void the warranty. Why not reset to default or remove and reinstall graphics card. AND leave things alone after.