all the steering components are problem as well as brake lines as mentined but the parts are dirt cheap. my yukon had all these issues so i got it for half of what everyone else wanted. i redid every steering peice including the box for 250. the brakes i got a couple coils of line, fittings, and the metric tool for less than 100.
the tbi engines are really good on gas, i kinda wish i still had my old 89 350 in this yukon. the power gain from the vortec is not worth the complexity and mileage loss.
the transmissions are an issue but again ive found places that will rebuild it for relatively cheap and if your rebuilder knows the upgrades and you put a cooler on it you only have to do it once.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock