Welcome!
To help answer your question, the platform for your 'burb did come out in 1988. However, GM continued to make the old body style (73-87) trucks in the cab and chassis, Blazer, and Suburban lines up through 1991.
So, if the bumper came off a 1990 1/2 or 3/4 ton, you know you're safe. If it came off a 1 ton, you'll need to find out which body style it was.
Casey
1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter