my tahoe started surging about 300 rpms while accelerating. it does it a lot, every few seconds and especially when going uphill. it kind of feels like its slipping but its not. ive changed tps, plugs, and fuel filter. cleaned tb and iac. done check for vacuum leaks too. also, there has been no engine light come on. .What could be doing this because its costing me gas and driving me crazy? please give me some advice