Rough idle, check engine light flashing after replacing crankshaft sensor

Before I replaced the crankshaft sensor it would always take a couple turns of the key to make it start, once it would start if I drove at a low speed limit it ran alright. However, if I hopped on the highway going 65+ for more than a few minutes then came back down to slower in town speeds it would start idling rough, then the oil gauge was fluctuating same as the battery gauge with my lights dimming in and out like it was going to shut off. So I replaced the crankshaft sensor, once I did that it would start up with the first turn of the key and drove normal, but now if I get on the highway once I get at a high speed limit it starts running rough and now the check engine light flashes. I had a new fuel pump replaced not too long ago. So any help is much appreciated.